Work Vehicle Transmission and Work Vehicle Having the Same

ABSTRACT

A work vehicle transmission includes a first transmission mechanism that changes input motive power to any one of multiple speeds, and a second transmission mechanism that changes the motive power changed by the first transmission mechanism to any one of multiple speeds, the number of speeds of the second transmission mechanism being smaller than that of the first transmission mechanism. Multiple speed change multi-disc clutches of the first transmission mechanism are arranged parallel with multiple deceleration multi-disc clutches of the second transmission mechanism so as to be adjacent in the diameter direction thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Applications Nos.2017-122616, 2017-122617, 2017-122618, 2017-122619, 2017-122620,2017-122621 and 2017-122622, each filed on Jun. 22, 2017, thedisclosures of which are hereby incorporated in their entirety byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a work vehicle transmission and a workvehicle having the same. The work vehicle according to the invention istypically a tractor, but not limited thereto.

2. Description of the Related Art (1) First Related Art

A work vehicle transmission disclosed in JP 2001-105912A includesmultiple transmission shafts that extend parallel with each other in thefront-rear direction of the vehicle body, and a multistage transmissionapparatus, which includes a first transmission mechanism that changesinput motive power between multiple speeds, and a second transmissionmechanism that changes the motive power changed by the firsttransmission mechanism between a smaller number of speeds than the firsttransmission mechanism.

This transmission is sometimes configured to be capable of changingbetween a total of eight speeds by including a main transmissionapparatus that can change between first to fourth speeds by theengagement and disengagement operations of four multi-disc clutches(hydraulic clutches) and an auxiliary transmission apparatus that canchange between a high speed and a low speed by the engagement anddisengagement operations of two multi-disc clutches (hydraulicclutches). Also, in this work vehicle transmission, the maintransmission apparatus and the auxiliary transmission apparatus, whichenable changing between eight speeds overall, are arranged so as to beseparated in the front-rear direction on the front side and rear side ofthe transmission case.

With this configuration, given that the main transmission apparatus andthe auxiliary transmission apparatus are arranged so as to be separatedin the front-rear direction, the operation systems for the maintransmission apparatus and the auxiliary transmission apparatus thatenable changing between eight speeds are also configured so as to beseparated in the front-rear direction. For this reason, the operationsystems for the main transmission apparatus and the auxiliarytransmission apparatus become complex, thus making it troublesome toconfigure the operation systems.

In view of this, there is desire for the ability to easily configure theoperation systems for the multistage transmission apparatus.

(2) Second Related Art

A work vehicle transmission disclosed in JP H8-2267A (or correspondingU.S. Pat. No. 5,599,247) includes a transmission case that also servesas an oil tank, multiple hydraulic devices arranged inside thetransmission case, and a valve unit that controls the flow of oil withrespect to the hydraulic devices.

In this transmission, an opening is provided in one side wall of thetransmission case (front portion housing), and the valve unit (controlvalve apparatus) for controlling operations of the auxiliarytransmission apparatus is fixed and supported to the transmission casein a state of being inserted through the opening and spanning the insideand outside of the transmission case.

With this configuration, the strength of the transmission case decreasesdue to providing the opening in the one side wall of the transmissioncase. Also, in the case where the valve unit has electromagnetic valves,iron powder or the like contained in the oil stored inside thetransmission case is drawn toward the valve unit by excitation of theelectromagnetic valves, and there is a risk that the iron powder willenter the valve unit and become lodged in an electromagnetic valve,which leads to problems.

In view of this, there is desire to be able to prevent iron powder orthe like contained in the oil in the transmission case from adverselyinfluencing the valve unit, while also preventing a decrease in thestrength of the transmission case.

SUMMARY OF THE INVENTION

(1a) The following work vehicle transmission is proposed in light of thefirst related art.

A work vehicle transmission including:

a plurality of transmission shafts that extend parallel with each otherin a front-rear direction of a vehicle body, the plurality oftransmission shafts including a speed change shaft and a decelerationshaft; and

a multi-stage transmission apparatus including:

-   -   a first transmission mechanism configured to change input motive        power to any one of a plurality of speeds, the first        transmission mechanism having a plurality of speed change gear        sets, and a plurality of speed change multi-disc clutches that        are arranged adjacent in the front-rear direction on the speed        change shaft and engage and disengage power transmission to the        plurality of speed change gear sets; and    -   a second transmission mechanism configured to change motive        power changed by the first transmission mechanism to any one of        a plurality of speeds, the number of speeds of the second        transmission mechanism being smaller than the number of speeds        of the first transmission mechanism, and the second transmission        mechanism having a plurality of deceleration gear sets, and a        plurality of deceleration multi-disc clutches that are arranged        on the deceleration shaft and engage and disengage power        transmission to the plurality of deceleration gear sets,

wherein the plurality of speed change multi-disc clutches are arrangedparallel with the plurality of deceleration multi-disc clutches so as tobe adjacent in a diameter direction thereof.

According to this configuration, the speed change multi-disc clutchesand the deceleration multi-disc clutches are arranged in a groupedmanner so as to be adjacent in their diameter direction or thefront-rear direction, and therefore the operation systems for the speedchange multi-disc clutches and the deceleration multi-disc clutches canalso be easily configured in a grouped state.

Also, the number of speeds of the second transmission mechanism issmaller than the number of speeds of the first transmission mechanism,and therefore the number of deceleration multi-disc clutches in thesecond transmission mechanism is smaller than the number of speed changemulti-disc clutches in the first transmission mechanism. Furthermore,the deceleration multi-disc clutches engage and disengage high-torquemotive power that has been decelerated by the deceleration gear sets,and therefore have a stricter load condition than the speed changemulti-disc clutches that engage and disengage low-torque motive powerthat has not been decelerated. For this reason, the decelerationmulti-disc clutches are provided with a larger number of clutch platesthan the speed change multi-disc clutches, and have a longer length inthe axial direction (front-rear direction).

In consideration of this, in this transmission apparatus, the speedchange multi-disc clutches, which are more numerous but have a shorteraxial-direction length, are arranged coaxially with the speed changeshaft and adjacent in the front-rear direction. Also, the decelerationmulti-disc clutches, which are less numerous but have a longeraxial-direction length, are arranged coaxially with the decelerationshaft and adjacent in the front-rear direction.

Accordingly, the length of the transmission apparatus in the axialdirection (the front-rear direction) can be set shorter than in the casewhere, for example, the speed change multi-disc clutches having ashorter axial-direction length are separated and arranged coaxially withthe speed change shaft and coaxially with the deceleration shaft andadjacent in the front-rear direction, and the deceleration multi-discclutches having a longer axial-direction length are arranged adjacent inthe front-rear direction and coaxially with the deceleration shaft alongwith several of the speed change multi-disc clutches.

As a result, it is possible to shorten the front-rear length of the workvehicle transmission that includes this transmission apparatus, whilealso making it possible to easily configure the operation systems forthe multi-disc clutches of the transmission apparatus.

In a preferable aspect, the plurality of transmission shafts includes anintermediate shaft arranged between the speed change shaft and thedeceleration shaft.

According to this configuration, the speed change gear sets thattransmit motive power from the speed change shaft to the intermediateshaft can each be constituted by a first speed change gear arrangedcoaxially with the speed change shaft and a second speed change geararranged coaxially with the intermediate shaft. Also, the decelerationgear sets that transmit motive power from the intermediate shaft to thedeceleration shaft can each be constituted by a first deceleration geararranged coaxially with the intermediate shaft and a second decelerationgear arranged coaxially with the deceleration shaft. In other words, thespeed change gear sets and the deceleration gear sets can each beconstituted by the minimum number of gears (two). As a result, it ispossible to achieve compactness, configuration simplification and thelike for the transmission apparatus through a reduction in the number ofparts.

In a preferable aspect, the speed change shaft, the deceleration shaftand the intermediate shaft are arranged forming an isosceles trianglehaving the intermediate shaft as an upper vertex in a front view of thevehicle body.

According to this configuration, in the transmission apparatus, thespeed change shaft and the deceleration shaft, which are heavier due tothe speed change multi-disc clutches and the deceleration multi-discclutches being arranged coaxially, are arranged side-by-side in theright-left direction in the lower portion of the transmission apparatus.Also, the intermediate shaft, which is lighter due to the speed changemulti-disc clutches and the deceleration multi-disc clutches not beingarranged coaxially, is arranged at a position that is between the speedchange shaft and the deceleration shaft and is higher the speed changeshaft and the deceleration shaft. In other words, the transmissionapparatus can be provided in the work vehicle transmission with a lowcenter of gravity and improved balance in the right-left direction, anddue to lowering the center of gravity of the work vehicle transmissionand improving the balance in the right-left direction, it is possible toimprove the stability of the work vehicle transmission.

In a preferable aspect, diameter-direction sizes of the plurality ofspeed change multi-disc clutches and the plurality of decelerationmulti-disc clutches are set to the same size.

According to this configuration, clutch plates (drive plates and drivenplates), pressure plates, pistons and the like that are used in thespeed change multi-disc clutches and the deceleration multi-discclutches can be common parts that are used in common in these multi-discclutches that all have the same diameter-direction size. As a result, itis possible to facilitate parts management, for example.

Also, when controlling the engagement and disengagement operations ofthe speed change multi-disc clutches and the deceleration multi-discclutches by electro-hydraulic control, given that the pistons and thelike are common parts, by setting the same initial pressure for thespeed change multi-disc clutches and the deceleration multi-discclutches, it is possible to set the same clutch meet timing for thesemulti-disc clutches. As a result, it is easier to create various controlprograms that are necessary for appropriately controlling the engagementand disengagement operations of the speed change multi-disc clutches andthe deceleration multi-disc clutches by electro-hydraulic control.

The present invention is also directed to a work vehicle equipped withthe work vehicle transmission having any one of the aboveconfigurations, and in the case of this work vehicle, it is possible tosuppress an increase in the size of the work vehicle that tends to havea long front-rear length, and it is also possible to improve thestability of the work vehicle.

(1b) Furthermore, the following work vehicle transmission is proposed inlight of the first related art.

A work vehicle transmission including:

a plurality of transmission shafts that extend parallel with each otherin a front-rear direction of a vehicle body, the plurality oftransmission shafts including a speed change shaft and a decelerationshaft; and

a multi-stage transmission apparatus including:

-   -   a first transmission mechanism configured to change input motive        power to any one of a plurality of speeds, the first        transmission mechanism having a plurality of speed change gear        sets, and a plurality of speed change multi-disc clutches that        are arranged adjacent in the front-rear direction on the speed        change shaft and engage and disengage power transmission to the        plurality of speed change gear sets; and    -   a second transmission mechanism configured to change motive        power changed by the first transmission mechanism to any one of        a plurality of speeds, the number of speeds of the second        transmission mechanism being smaller than the number of speeds        of the first transmission mechanism, and the second transmission        mechanism having a plurality of deceleration gear sets, and a        plurality of deceleration multi-disc clutches that are arranged        on the deceleration shaft and engage and disengage power        transmission to the plurality of deceleration gear sets,

wherein the plurality of transmission shafts further includes anintermediate shaft arranged between the speed change shaft anddeceleration shaft, the speed change multi-disc clutches and thedeceleration multi-disc clutches not being arranged coaxially with theintermediate shaft, and

in a front view of the vehicle body, assuming that there are formed apair of triangular virtual spaces that each has, as one side, a virtualline interconnecting an axis of the speed change shaft and an axis ofthe deceleration shaft and that are above and below the virtual line,the intermediate shaft is inserted into one of the virtual spaces.

According to this configuration, the speed change multi-disc clutchesand the deceleration multi-disc clutches are arranged in a groupedmanner so as to be adjacent in the front-rear direction and coaxial withthe speed change shaft and the deceleration shaft respectively, andtherefore the operation systems for the speed change multi-disc clutchesand the deceleration multi-disc clutch can also be easily configured ina grouped state.

Also, the number of speeds of the second transmission mechanism issmaller than the number of speeds of the first transmission mechanism,and therefore the number of deceleration multi-disc clutches in thesecond transmission mechanism is smaller than the number of speed changemulti-disc clutches in the first transmission mechanism. Furthermore,the deceleration multi-disc clutches engage and disengage high-torquemotive power that has been decelerated by the deceleration gear sets,and therefore have a stricter load condition than the speed changemulti-disc clutches that engage and disengage low-torque motive powerthat has not been decelerated. For this reason, the decelerationmulti-disc clutches are provided with a larger number of clutch platesthan the speed change multi-disc clutches, and have a longer length inthe axial direction (front-rear direction).

In consideration of this, in this transmission apparatus, the speedchange multi-disc clutches, which are more numerous but have a shorteraxial-direction length, are arranged coaxially with the speed changeshaft and adjacent in the front-rear direction. Also, the decelerationmulti-disc clutches, which are less numerous but have a longeraxial-direction length, are arranged coaxially with the decelerationshaft and adjacent in the front-rear direction.

Accordingly, the length of the transmission apparatus in the axialdirection (the front-rear direction) can be set shorter than in the casewhere, for example, the speed change multi-disc clutches having ashorter axial-direction length are separated and arranged coaxially withthe speed change shaft and coaxially with the deceleration shaft andadjacent in the front-rear direction, and the deceleration multi-discclutches having a longer axial-direction length are arranged adjacent inthe front-rear direction and coaxially with the deceleration shaft alongwith several of the speed change multi-disc clutches.

Also, effective use is made of the substantially triangular pair ofspaces formed between the speed change multi-disc clutches and thedeceleration multi-disc clutches, and the intermediate shaft is insertedinto one of these spaces, thus making it possible to shorten the lengthof the transmission apparatus in a direction (up-down direction orright-left direction) that is orthogonal to the axial direction(front-rear direction).

As a result, it is possible to shorten the front-rear length as well asthe up-down length or right-left length of the work vehicle transmissionthat includes this transmission apparatus, while also making it possibleto easily configure the operation systems for the multi-disc clutches ofthe transmission apparatus.

In a preferable aspect, the plurality of speed change multi-discclutches and the plurality of deceleration multi-disc clutches arearranged so as to be adjacent in a right-left direction of the vehiclebody, and

in a front view of the vehicle body, the pair of virtual spaces arerespectively formed above and below a position between the speed changemulti-disc clutches and the deceleration multi-disc clutches.

According to this configuration, effective use is made of thesubstantially triangular pair of upper and lower spaces formed betweenthe speed change multi-disc clutches and the deceleration multi-discclutches, and the intermediate shaft is inserted into one of thesespaces, thus making it possible to shorten the length of thetransmission apparatus in the up-down direction.

As a result, it is possible to shorten the front-rear length and theup-down length of the work vehicle transmission that includes thistransmission apparatus, while also making it possible to easilyconfigure the operation systems for the multi-disc clutches of thetransmission apparatus.

In a preferable aspect, the work vehicle transmission further includes:

a drive switching apparatus that includes a multi-disc clutch and isconfigured to switch a transmission state with respect to right and leftfront wheels by an engaging/disengaging operation of the multi-discclutch,

wherein the drive switching apparatus is arranged below the transmissionapparatus in a state where an upper portion of the multi-disc clutch isinserted into the virtual space on a lower side in the front view of thevehicle body.

According to this configuration, it is possible to shorten the up-downlength of the work vehicle transmission, while also arranging the driveswitching apparatus below the transmission apparatus. It is alsopossible to lower the center of gravity of the work vehicle transmissioncompared to the case where the drive switching apparatus is arrangedabove the transmission apparatus.

In a preferable aspect, diameter-direction sizes of the plurality ofspeed change multi-disc clutches and the plurality of decelerationmulti-disc clutches are set to the same size.

According to this configuration, clutch plates (drive plates and drivenplates), pressure plates, pistons and the like that are used in thespeed change multi-disc clutches and the deceleration multi-discclutches can be common parts that are used in common in these multi-discclutches that all have the same diameter-direction size. As a result, itis possible to facilitate parts management, for example.

Also, when controlling the engagement and disengagement operations ofthe speed change multi-disc clutches and the deceleration multi-discclutches by electro-hydraulic control for example, given that thepistons and the like are common parts, by setting the same initialpressure for the speed change multi-disc clutches and the decelerationmulti-disc clutches, it is possible to set the same clutch meet timingfor these multi-disc clutches. As a result, it is easier to createvarious control programs that are necessary for appropriatelycontrolling the engagement and disengagement operations of the speedchange multi-disc clutches and the deceleration multi-disc clutches byelectro-hydraulic control.

The present invention is also directed to a work vehicle equipped withthe work vehicle transmission having any one of the aboveconfigurations, and in the case of this work vehicle, it is possible tosuppress an increase in the size of the work vehicle that tends to havea long front-rear length, and it is also possible to improve thestability of the work vehicle.

(2) The following work vehicle transmission is proposed in light of thesecond related art.

A work vehicle transmission including:

a transmission case that also serves as an oil tank;

a plurality of hydraulic devices arranged inside the transmission case;and

a valve unit configured to control a flow of oil to the hydraulicdevices,

wherein the transmission case includes a valve unit attachment portionto which the valve unit is to be attached from outside the transmissioncase,

the valve unit has a base plate to be attached to the valve unitattachment portion, and a valve block having a plurality ofelectromagnetic valves, and

the valve unit attachment portion is provided with a recessed portionthat defines and forms a storage compartment for the valve block alongwith the base plate.

According to this configuration, in the state where the valve unit isattached to the valve unit attachment portion, the valve block is storedin the storage compartment defined and formed outside of thetransmission case. Accordingly, it is possible to prevent iron powder orthe like contained in the oil in the transmission case from being drawntoward the valve unit by excitation of the electromagnetic valves. As aresult, it is possible to avoid the risk that, due to this drawing, theiron powder or the like contained in the oil inside the transmissioncase enters the valve unit and becomes lodged in any one of theelectromagnetic valves.

Also, there is no need for an opening for allowing the valve block toenter the interior space of the transmission case to be formed in thevalve unit attachment portion in the case where the valve block isarranged in the interior space of the transmission case, thus making itpossible to prevent a reduction in the strength of the transmission casecaused by the formation of such an opening.

In a preferable aspect, the valve unit attachment portion includes anoil return passage configured to return excess oil from the valve blockinto the transmission case at a position higher, with respect to avertical direction of the vehicle body, than the valve block in therecessed portion.

According to this configuration, oil that has leaked from theelectromagnetic valves of the valve block can be stored as lubricatingoil up to a position in the storage compartment higher, with respect tothe vehicle body vertical direction, than the valve block. In the casewhere the oil surface of this lubricating oil reaches the location ofthe oil return passage of the storage compartment, the lubricating oilat the location of the oil return passage can be returned as excess oilto the inside of the transmission case via the oil return passage. It isalso possible to make it unlikely for a problem to occur in which oilstored inside the transmission case, as well as iron powder or the likecontained in such oil, flows from the oil return passage into thestorage compartment due to, for example, large inclination of the workvehicle provided with this transmission. As a result, it is possible toreturn excess oil in the storage compartment to the transmission case,while also preventing the risk of iron powder or the like contained inthe oil in the transmission case from becoming lodged in anelectromagnetic valve.

In a preferable aspect, a plurality of the oil return passages areformed in two sections vertically in the valve unit attachment portion.

According to this configuration, compared to the case where the oilreturn passages are not divided into two sections vertically and havethe same opening area, it is possible to make it unlikely for a problemto occur in which oil in the transmission case, as well as iron powderor the like contained in such oil, flows from the oil return passagesinto the storage compartment. As a result, it is possible to returnexcess oil in the storage compartment to the transmission case, whilealso more reliably avoiding the risk of iron powder or the likecontained in the oil in the transmission case becoming lodged in anelectromagnetic valve.

In a preferable aspect, the oil return passages are formed such that anopening area of the oil return passage in an upper section is smallerthan an opening area of the oil return passage in a lower section.

According to this configuration, when the amount of oil leaking from theelectromagnetic valves is small, the excess oil in the storagecompartment can be quickly returned to the transmission case through theoil return passage in the lower section that has a large opening area,and when the amount of oil leaking from the electromagnetic valves islarge, the excess oil in the storage compartment can be quickly returnedto the transmission case through the oil return passages in the twoupper and lower sections. Also, due to setting a smaller opening areafor the oil return passage in the upper section, which is used as anauxiliary passage for when a large amount of oil leaks from theelectromagnetic valves, it is possible to prevent a reduction in thestrength of the transmission case that occurs due to unnecessarilyincreasing the opening area of the oil return passage in the uppersection.

In a preferable aspect, the recessed portion has a lower recessionportion in which the valve block is stored, and an upper recessionportion that is in communication with an interior of the transmissioncase via the oil return passage, and

the upper recession portion is formed with a shallower recession depththan the lower recession portion and a smaller area than the lowerrecession portion.

According to this configuration, the interior space of the transmissioncase can be larger than in the case where, for example, the upperrecession portion not storing the valve block is formed so as to havethe same recession depth and area as the lower recession portion. As aresult, it is easier to perform arrangement, assembly and the like ofthe transmission systems that are to be arranged in the interior spaceof the transmission case.

Furthermore, due to the recession depth of the lower recession portionbeing deeper than the recession depth of the upper recession portion,the valve block can be stored in the storage compartment even in thecase where the thickness of the valve block increases due to having alarge electromagnetic valve, or the case where the valve block isconfigured with a two-layer stacked structure due to an increase in thenumber of provided electromagnetic valves, for example.

In a preferable aspect, an oil filter is provided in the oil returnpassage.

According to this configuration, even if oil stored inside thetransmission case flows through the oil return passages to the storagecompartment, it is possible to prevent iron powder or the like containedin such oil from flowing into the storage compartment. Also, because theoil return passages are formed in two sections vertically as previouslydescribed, in the case where a clog forms at the oil filter provided inthe oil return passage in the lower section, excess oil in the storagecompartment can be returned to the inside of the transmission casethrough the oil return passage in the upper section.

In a preferable aspect, the plurality of electromagnetic valves includesa plurality of electromagnetic on/off valves and a plurality ofelectromagnetic proportional valves,

the valve block includes a first valve block that has the plurality ofelectromagnetic on/off valves, and a second valve block that has theplurality of electromagnetic proportional valves,

the first valve block is attached to a storage compartment formingsurface of the base plate that forms the storage compartment along withthe recessed portion, and

the second valve block is attached to an outer surface of the base plateon a side opposite to the storage compartment forming surface.

According to this configuration, oil that has leaked from anelectromagnetic on/off valve that has a high risk of oil leakage can bestored in the storage compartment as lubricating oil, and it is possibleto prevent such oil from leaking to the outside. Also, compared to thecase where all of the electromagnetic valves, including anelectromagnetic proportional valve that has a low risk of oil leakage,are stored in the storage compartment, it is possible to reduce the sizeof the recessed portion formed in the transmission case for storing thestorage compartment, and it is possible to increase the size of theinterior space of the transmission case. As a result, it is easier toperform arrangement, assembly and the like of the transmission systemsand the like that are to be arranged in the interior space of thetransmission case.

In a preferable aspect, a partition wall is formed as a single piecewith the transmission case, the partition wall supporting the pluralityof transmission shafts provided in the transmission case,

the plurality of hydraulic devices includes a plurality of transmissionswitching apparatuses arranged on the plurality of transmission shafts,

the valve unit attachment portion is formed at a predetermined positionin a front-rear direction of the vehicle body at which the partitionwall is formed in the transmission case, and

the partition wall is provided with a plurality of inner oil passagesthat extend between a plurality of connection ports formed in the valveunit and a plurality of oil passages formed in the plurality oftransmission shafts.

According to this configuration, in the formation of the hydraulicpassages between the valve unit and the transmission switchingapparatuses, there is no need to assemble hydraulic tubes inside thetransmission case. Also, the inner oil passages of the partition wallthat extend between the connection ports of the valve unit and the oilpassages of the transmission shafts can be formed with a simple straightshape and with a minimum length. As a result, it is possible to reducethe number of work steps required to form the hydraulic passages for thetransmission switching apparatuses. Also, due to forming the inner oilpassages of the partition wall with a simple straight shape and with aminimum length, the hydraulic passages extending between the valve unitand the transmission switching apparatuses can be formed with a simpleshape and with a minimum length. As a result, it is possible to improvethe response of the transmission switching apparatuses.

The present invention is also directed to a work vehicle equipped withthe work vehicle transmission having any one of the aboveconfigurations, and in the case of this work vehicle, it is possible tomake it less likely for a problem to occur with an electromagnetic valvedue to iron powder or the like contained in the oil in the transmissioncase, and to prevent a reduction in the strength of the transmissioncase.

(3) The configurations proposed in sections (1a), (1b), and (2) abovecan be implemented on their own, and can also be implemented inappropriate combinations as long as no contradiction arises.

Other features and advantages achieved thereby will become apparent fromthe description given below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a left side view of a tractor;

FIG. 2 is a schematic view of a work vehicle transmission and the likeshowing a drive system of the tractor;

FIG. 3 is a plan view in transverse section of the work vehicletransmission showing the drive system of the tractor;

FIG. 4 is a plan view in transverse section of a relevant portionshowing a configuration of a first transmission mechanism in a maintransmission apparatus;

FIG. 5 is a plan view in transverse section of a relevant portionshowing a configuration of a creep transmission apparatus and a secondtransmission mechanism of the main transmission apparatus;

FIG. 6 is a left side view in vertical section of a relevant portionshowing a configuration of a first speed change shaft side in anauxiliary transmission apparatus;

FIG. 7 is a left side view in vertical section of a relevant portionshowing a configuration of a second speed change shaft side in theauxiliary transmission apparatus;

FIG. 8 is a front view in vertical section of the work vehicletransmission showing the arrangement of a transmission shaft and thelike;

FIG. 9 is a front view in vertical section of the work vehicletransmission showing the shapes and the like of a valve unit attachmentportion and a storage compartment;

FIG. 10 is a perspective view of the valve unit attachment portion inthe work vehicle transmission;

FIG. 11 is a view in section taken along XII-XII in FIG. 9 (a left sideview in vertical section of the valve unit attachment portion);

FIG. 12 is a right side view of the valve unit;

FIG. 13 is a left side view in vertical section of a relevant portionshowing a state where the transmission case is divided into front andrear portions at the arrangement location of the creep transmissionapparatus;

FIG. 14 is a diagram corresponding to FIG. 5, showing a creeptransmission apparatus according to another embodiment; and

FIG. 15 is a diagram corresponding to FIG. 13, showing the creeptransmission apparatus according to the embodiment in FIG. 14.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following describes, with reference to the drawings, an embodimentin which a work vehicle transmission according to the present inventionis applied to a tractor, which is one example of a work vehicle, as oneaspect for carrying out the present invention.

Note that the direction indicated by the arrow denoted by “F” in FIGS. 1and 11 is the front side of the tractor, and the direction indicated bythe arrow denoted by “U” is the upper side of the tractor.

Overall Configuration of Tractor

As shown in FIG. 1, the tractor according to the present embodimentincludes: a motor power portion 1 that is arranged in the front halfportion of the vehicle body; a boarding-type driver portion 2 and a workvehicle transmission 3 (simply referred to as “the transmission 3”hereinafter) that are arranged in the rear half portion of the vehiclebody; a fuel tank 4 that is arranged on the left side of thetransmission 3; right and left front wheels 5 that are drivably andsteerably arranged on the right and left sides of the motor powerportion 1; right and left rear wheels 6 that are drivably arranged onthe right and left sides of the transmission 3; a link mechanism 7 forwork apparatus coupling that is elevatably and swingably attached to therear end portion of the transmission 3, etc.

The motor power portion 1 includes: a front portion frame 8 that isarranged on the front portion side of the vehicle body; an engine 9 thatis supported to the rear portion side of the front portion frame 8; ahood 10 that is pivotally opened and closed to cover the engine 9 andthe like, etc. The engine 9 has an output shaft 9A (see FIG. 2) thatprojects rearward toward the transmission 3 on the rear side.

The driver portion 2 includes: a cabin 11 that is supported on thetransmission 3 in a vibration-controlled manner; a steering wheel 12that is arranged on the front side in the cabin 11 for steering thefront wheels 5; and a driver seat 13 that is arranged on the rear sidein the cabin 11, etc.

Transmission and Transmission Case

As shown in FIGS. 1 to 3, the transmission 3 includes: a transmissioncase 14 that serves as both the rear portion frame of the vehicle bodyand an oil tank; an input shaft 15 that receives motive power from theengine 9; a first output shaft 16 that is for the front wheels andoutputs motive power for driving the front wheels; right and left secondoutput shafts 17 that are for the rear wheels and output motive powerfor driving the rear wheels 6; a PTO (power takeoff) shaft 18 thatoutputs motive power for a work operation (work-implement operation); atraveling transmission system 19 that transmits motive power received bythe input shaft 15 to the first output shaft 16 and the right and leftsecond output shafts 17; a work (work-implement) transmission system 20that transmits motive power received by the input shaft 15 to the PTOshaft 18, etc. The axial directions of the first output shaft 16 and thePTO shaft 18 are set to the front-rear direction of the vehicle body.The axial directions of the right and left second output shafts 17 areset to the right-left direction of the vehicle body.

The transmission case 14 includes: a first case 21 that is bolt-coupledto the rear end of the engine 9; a second case 22 that is bolt-coupledto the rear end of the first case 21; a third case 23 that isbolt-coupled to the rear end of the second case 22; a fourth case 24that is bolt-coupled to the rear end of the third case 23; a fifth case25 that is bolt-coupled to the lower end of the second case 22; rightand left sixth cases 26 that are respectively bolt-coupled to the rightand left ends of the fourth case 24, etc. In other words, thetransmission case 14 is configured with a seven-part divided structurecapable of being divided into the seven cases 21 to 26. The second case22 includes: a front cover 27 that is bolt-coupled to an inner flange22A; and a first support wall 28 that is bolt-coupled to the rear end ofthe second case 22. A partition wall 22B is formed as a single piecewith the second case 22 and divides the interior space thereof into afront space and a rear space. The third case 23 includes a secondsupport wall 29 that is bolt-coupled with a coupling portion 23Aprovided therein. A separation wall 23B is formed as a single piece withthe rear end of the third case 23 and separates the interior spacethereof from the interior space of the fourth case 24. The fourth case24 includes a rear cover 30 that is bolt-coupled to the rear endthereof.

Traveling Transmission System

As shown in FIGS. 2 to 9, the traveling transmission system 19 includes:an electro-hydraulic controllable forward/rearward switchover apparatus31 (one example of a transmission switching apparatus) that isconfigured to switch motive power received by the input shaft 15 betweenmotive power for forward travel and motive power for rearward travel; anelectro-hydraulic controllable main transmission apparatus 32 (oneexample of a transmission apparatus, and one example of a transmissionswitching apparatus) that changes traveling motive power from theforward/rearward switchover device 31 to one of eight (8) speeds; acreep transmission apparatus 33 that changes traveling motive power fromthe main transmission apparatus 32 to one of two (2) speeds; anauxiliary transmission apparatus 34 that changes traveling motive powerfrom the creep transmission apparatus 33 to one of three (3) speeds; adistributor shaft 35 that distributes traveling motive power from theauxiliary transmission apparatus 34 forward and rearward; a decelerationgear set 36 that decelerates traveling motive power distributed by thedistributor shaft 35 into front wheel driving motive power; anelectro-hydraulic controllable drive switching unit 37 that switches thetransmission state from the deceleration gear set 36 to the first outputshaft 16; a rear wheel differential apparatus 38 that distributestraveling motive power from the distributor shaft 35 to the right andleft rear wheels 6 while allowing differential power between the rightand left rear wheels 6; right and left planetary gear decelerationapparatuses 39 that decelerate traveling motive power from the rearwheel differential apparatus 38 into rear wheel driving motive power;right and left side brakes 40 that apply braking force to right and leftdifferential shafts 38A of the rear wheel differential apparatus 38,etc.

The rear wheel differential apparatus 38 includes a hydraulicdifferential switching mechanism 38B that switches the operation statebetween a differential allowed state and a differential stopped state.The right and left planetary gear deceleration apparatuses 39 deceleratemotive power and transmit it to the right and left rear wheels 6 via theright and left second output shafts 17.

As shown in FIG. 1, front wheel driving motive power from the firstoutput shaft 16 is transmitted to the right and left front wheels 5 viaan external transmission shaft 41 that rotates integrally with the firstoutput shaft 16, and a front wheel differential apparatus (not shown)that distributes front wheel driving motive power from the externaltransmission shaft 41 to the right and left front wheels 5 whileallowing differential power between the right and left front wheels 5.The front wheel differential apparatus includes a hydraulic differentialswitching mechanism that switches the operation state thereof betweenthe differential allowed state and the differential stopped state.

Work Transmission System

As shown in FIGS. 2, 3 and 8, the work transmission system 20 includes:an upstream relay shaft 42 and a downstream relay shaft 43 that are forwork motive power transmission and are arranged coaxially with the inputshaft 15 in a state of rotating integrally with the input shaft 15; anda work motive power switching apparatus 44 (one example of atransmission switching apparatus) that switches the transmission statefrom the downstream relay shaft 43 to the PTO shaft 18.

Forward/Rearward Switchover Apparatus

As shown in FIGS. 2, 3 and 9, the forward/rearward switchover apparatus31 includes: a forward multi-disc clutch 45 and a rearward multi-discclutch 46 that are arranged coaxially with the input shaft 15; acounter-rotation shaft 47 that is arranged parallel with the input shaft15 at a position below the input shaft 15; a forward output gear 48 bywhich motive power received via the forward multi-disc clutch 45 isoutputted as forward motive power; a counter-rotation gear set 49 bywhich motive power received via the rearward multi-disc clutch 46 istransmitted to the counter-rotation shaft 47; a reverse output gear 50that outputs counter-rotation motive power from the counter-rotationshaft 47 as reverse motive power, etc. In other words, theforward/rearward switchover apparatus 31 employs a multi-disc clutchtype of transmission switching apparatus that switches the transmissionstate by the engagement and disengagement operations of the two, forwardand rearward multi-disc clutches 45, 46.

The forward/rearward switchover apparatus 31 is arranged in the frontspace inside the second case 22, wherein the front end side of the inputshaft 15 and the front end portion of the counter-rotation shaft 47 aresupported by the front cover 27, and the rear end portion of the inputshaft 15 and the rear end portion of the counter-rotation shaft 47 aresupported by the partition wall 22B of the second case 22.

Main Transmission Apparatus

As shown in FIGS. 2 to 5, 8 and 9, the main transmission apparatus 32has an eight-speed transmission configuration including: a firsttransmission shaft 51 for input (one example of a speed change shaft); asecond transmission shaft 52 for relay (one example of an intermediateshaft); a third transmission shaft 53 for output (one example of adeceleration shaft); a first transmission mechanism 54 that changesmotive power input to the first transmission shaft 51 between four (4)speeds; and a second transmission mechanism 55 that changes the motivepower, having changed by the first transmission mechanism 54, betweentwo, high and low speeds. The first transmission mechanism 54 includes:four (4) speed change gear sets 56 to 59 that transmit motive power fromthe first transmission shaft 51 to the second transmission shaft 52 withdifferent transmission ratios; and four (4) speed change multi-discclutches 60 to 63 that engage/disengage power transmission to thecorresponding speed change gear sets 56 to 59. The second transmissionmechanism 55 includes: two deceleration gear sets 64, 65 that transmitmotive power from the second transmission shaft 52 to the thirdtransmission shaft 53 with different transmission ratios; and twodeceleration multi-disc clutches 66, 67 that engage and disengage motivepower from the corresponding deceleration gear sets 64, 65. In otherwords, the main transmission apparatus 32 employs a multi-disc clutchtype of transmission switching apparatus that switches the transmissionstate by the engagement and disengagement operations of the four speedchange multi-disc clutches 60 to 63 and the two deceleration multi-discclutches 66, 67.

The main transmission apparatus 32 is arranged in the rear space insidethe second case 22, wherein the front end portions of the transmissionshafts 51 to 53 are supported by the partition wall 22B of the secondcase 22, and the rear end portions of the transmission shafts 51 to 53are supported by the first support wall 28.

In the main transmission apparatus 32, the three transmission shafts 51to 53 are arranged parallel in a state where the axial directionsthereof are set in the front-rear direction of the vehicle body. Thesecond transmission shaft 52A comprises a cylinder shaft that isrelatively rotatably fitted around the upstream relay shaft 42 of thework transmission system 20. The third transmission shaft 53 is arrangedcoaxially with and adjacent in the front-rear direction to the firstspeed change shaft 68 for input in the auxiliary transmission apparatus34.

As shown in FIGS. 2, 3 and 5, the creep transmission apparatus 33 isarranged between the third transmission shaft 53 of the maintransmission apparatus 32 and the first speed change shaft 68 of theauxiliary transmission apparatus 34 such that the third transmissionshaft 53 of the main transmission apparatus 32 is the upstreamtransmission shaft with respect to the creep transmission apparatus 33,and furthermore the first speed change shaft 68 of the auxiliarytransmission apparatus 34 is the downstream transmission shaft withrespect to the creep transmission apparatus 33.

Creep Transmission Apparatus

The creep transmission apparatus 33 includes: a deceleration mechanism69 that decelerates motive power from the third transmission shaft 53 ofthe main transmission apparatus 32; and a synchro mesh switchingmechanism 70 by which the transmission state of motive power from thethird transmission shaft 53 of the main transmission apparatus 32 to thefirst speed change shaft 68 of the auxiliary transmission apparatus 34is switched between a constant velocity state, in which motive powerfrom the third transmission shaft 53 is directly transmitted to thefirst speed change shaft 68, and a deceleration state in which it istransmitted via the deceleration mechanism 69. In other words, the creeptransmission apparatus 33 comprises a synchro mesh transmissionswitching apparatus that switches the transmission state by a switchingoperation performed by the synchro mesh switching mechanism 70.

The deceleration mechanism 69 employs a creep transmission mechanismthat decelerates motive power from the third transmission shaft 53 ofthe main transmission apparatus 32 to a super low speed via twodeceleration gear sets 71, 72 having a large transmission ratio.

Auxiliary Transmission Apparatus

As shown in FIGS. 2, 3, 6 and 7, the auxiliary transmission apparatus 34includes: the previously-described first speed change shaft 68; a secondspeed change shaft 73 that is arranged parallel with the first speedchange shaft 68; three (3) speed change gear sets 74 to 76 that transmitmotive power from the first speed change shaft 68 to the second speedchange shaft 73 with different transmission ratios; a synchro mesh firstswitching mechanism 77 that engages and disengages power transmissionfrom the first speed change shaft 68 to the high-speed deceleration gearset 72; a synchro mesh second switching mechanism 78 that engages anddisengages power transmission from the mid-speed and low-speed speedchange gear sets 75 and 76 to the second speed change shaft 73; and anoutput gear set 79 by which the changed motive power transmitted to thesecond speed change shaft 73 is outputted to the distributor shaft 35.In other words, the auxiliary transmission apparatus 34 employs asynchro mesh transmission switching apparatus that switches thetransmission state by a switching operation performed by the two synchromesh switching mechanisms 70.

The auxiliary transmission apparatus 34 is supported in the interiorspace of the third case 23, wherein the front end portion of the firstspeed change shaft 68 and the front end portion of the second speedchange shaft 73 are supported by the second support wall 29, andfurthermore the rear end portion of the first speed change shaft 68 andthe rear end portion of the second speed change shaft 73 are supportedby the separation wall 23B of the third case 23.

Drive Switching Unit

As shown in FIGS. 2, 8 and 9, the drive switching unit 37 includes: afront wheel transmission shaft 80 that is arranged parallel with thefirst output shaft 16 at a location directly above the first outputshaft 16; a first drive switching apparatus 81 for front wheel driving;and a second drive switching apparatus 82 for front wheel acceleration.The drive switching unit 37 is arranged spanning the rear space insidethe second case 22 and the interior space of the fifth case 25, whereinthe front end portion of the front wheel transmission shaft 80 aresupported by the partition wall 22B of the second case 22, the rear endportion of the front wheel transmission shaft 80 is supported by thefirst support wall 28, and the first output shaft 16 is supported by thefifth case 25.

The first drive switching apparatus 81 includes: a deceleration gear set83 by which front wheel driving motive power from the deceleration gearset 36 is decelerated for constant speed driving; and a constant speedtransmission multi-disc clutch 84 that engages and disengages powertransmission to the deceleration gear set 83. The deceleration gear set83 decelerates front wheel driving motive power such that the right andleft front wheels 5 are driven at the same circumferential speed as theright and left rear wheels 6, and transmits the decelerated motive powerfrom the front wheel transmission shaft 80 to the first output shaft 16.The constant speed transmission multi-disc clutch 84 switches between atransmission state in which the right and left front wheels 5 are drivenat the same circumferential speed as the right and left rear wheels 6,and a cut-off state in which the right and left front wheels 5 arerotated by propulsive force from the right and left rear wheels 6. Inother words, the first drive switching apparatus 81 employs a multi-discclutch transmission switching apparatus that switches the transmissionstate by the engagement and disengagement operation of the constantspeed transmission multi-disc clutch 84.

The second drive switching apparatus 82 includes: an acceleration gearset 85 by which front wheel driving motive power from the decelerationgear set 36 is accelerated for acceleration driving; and an accelerationtransmission multi-disc clutch 86 that engages and disengages powertransmission to the acceleration gear set 85. The acceleration gear set85 accelerates front wheel driving motive power such that the right andleft front wheels 5 are driven at approximately twice thecircumferential speed of the right and left rear wheels 6, and transmitsthe accelerated motive power from the front wheel transmission shaft 80to the first output shaft 16. The acceleration transmission multi-discclutch 86 switches between a transmission state in which the right andleft front wheels 5 are driven at approximately twice thecircumferential speed of the right and left rear wheels 6, and a cut-offstate in which the right and left front wheels 5 are rotated bypropulsive force from the right and left rear wheels 6. In other words,the second drive switching apparatus 82 employs a multi-disc clutchtransmission switching apparatus that switches the transmission state bythe engagement and disengagement operation of the accelerationtransmission multi-disc clutch 86.

In the drive switching unit 37, the constant speed transmissionmulti-disc clutch 84 and the acceleration transmission multi-disc clutch86 are arranged side-by-side in the front-rear direction coaxially withthe front wheel transmission shaft 80, wherein the constant speedtransmission multi-disc clutch 84 is supported on the front portion sideof the front wheel transmission shaft 80, and the accelerationtransmission multi-disc clutch 86 is supported on the rear portion sideof the front wheel transmission shaft 80.

Work Motive Power Switching Apparatus

As shown in FIGS. 2 and 3, the work motive power switching apparatus 44includes: a hydraulic PTO clutch 87 that engages and disengages workmotive power from the downstream relay shaft 43; a constant mesh firsttransmission mechanism 88 that changes motive power received via the PTOclutch 87 between two high and low speeds; and a constant mesh secondtransmission mechanism 89 that changes the motive power changed by thefirst transmission mechanism 88 between two high and low speeds. Amulti-disc clutch is employed as the PTO clutch 87. In other words, thework motive power switching apparatus 44 is a multi-disc clutch type ofconstant mesh transmission switching apparatus that switches thetransmission state by the engagement and disengagement operation of thework multi-disc clutch (PTO clutch 87) and the switching operationperformed by the two constant mesh transmission mechanisms 88, 89. Thework motive power switching apparatus 44 is arranged in the interiorspace of the fourth case 24 by being supported by the rear cover 30,etc.

According to the above configuration, the transmission 3 includes, as aplurality of transmission switching apparatuses each having a multi-discclutch configuration, the forward/rearward switchover apparatus 31 thathas the two, forward and rearward multi-disc clutches 45, 46; the maintransmission apparatus 32 that has the four speed change multi-discclutches 60 to 63 and the two deceleration multi-disc clutches 66, 67;the first drive switching apparatus 81 that has the constant speedtransmission multi-disc clutch 84; the second drive switching apparatus82 that has the acceleration transmission multi-disc clutch 86; and thework motive power switching apparatus 44 that has the work multi-discclutch (PTO clutch 87).

Multi-Disc Clutches of Main Transmission Apparatus

As shown in FIGS. 2 to 5 and 8, in the main transmission apparatus 32,the four speed change multi-disc clutches 60 to 63 are arrangedside-by-side in the front-rear direction coaxially with the firsttransmission shaft 51 that is arranged on the upstream side in thetransmission direction among the three transmission shafts 51 to 53 thatare arranged parallel with each other. Accordingly, the firsttransmission shaft 51 functions as a speed change shaft that supportsthe four speed change multi-disc clutches 60 to 63. The two decelerationmulti-disc clutches 66, 67 are arranged side-by-side in the front-reardirection coaxially with the third transmission shaft 53 that isarranged on the downstream side in the transmission direction among thethree transmission shafts 51 to 53 that are arranged parallel with eachother. Accordingly, the third transmission shaft 53 functions as adeceleration shaft that supports the two deceleration multi-discclutches 66, 67. Also, in the main transmission apparatus 32, the fourspeed change multi-disc clutches 60 to 63 arranged parallel with the twodeceleration multi-disc clutches 66, 67 in the right-left direction asshown in FIG. 8 (one example of the diameter direction) so that the fourspeed change multi-disc clutches 60 to 63 and the two decelerationmulti-disc clutches 66, 67 are arranged adjacent to (in alignment with)each other in the diameter direction thereof.

In other words, in the main transmission apparatus 32, the four speedchange multi-disc clutches 60 to 63 and the two deceleration multi-discclutches 66, 67 are arranged at the same position (in alignment) in thefront-rear direction of the vehicle body. Accordingly, compared to thecase where, for example, the four speed change multi-disc clutches 60 to63 and the two deceleration multi-disc clutches 66, 67 are arranged soas to be shifted at different positions in the front-rear direction ofthe vehicle body, the front-rear length of the main transmissionapparatus 32 can be set shorter, whereby the front-rear length of thetransmission 3 that includes this main transmission apparatus 32 can beset shorter. As a result, it is possible to prevent an increase in thesize of the tractor, which increases in overall length due to anincrease in the front-rear length of the transmission 3.

Transmission Shafts of Main Transmission Apparatus

As shown in FIGS. 2 and 8, in the main transmission apparatus 32, thesecond transmission shaft 52, which is one of the three transmissionshafts 51 to 53 that are arranged parallel with each other, is arrangedas an intermediate shaft between the first transmission shaft 51 (speedchange shaft) and the third transmission shaft 53 (deceleration shaft).

Accordingly, the four speed change gear sets 56 to 59 that transmitmotive power from the first transmission shaft 51 to the secondtransmission shaft 52 can be respectively constituted by first speedchange gears 56A to 59A that are arranged coaxially with the firsttransmission shaft and second speed change gears 56B to 59B that arearranged coaxially with the second transmission shaft 52. Also, the twodeceleration gear sets 64, 65 that transmit motive power from the secondtransmission shaft 52 to the third transmission shaft 53 can berespectively constituted by first deceleration gears 64A, 65A that arearranged coaxially with the second transmission shaft 52 and seconddeceleration gears 64B, 65B that are arranged coaxially with the thirdtransmission shaft 53.

In other words, the four speed change gear sets 56 to 59 and the twodeceleration gear sets 64, 65 can each be constituted by the smallestnumber of gears (two gears). As a result, it is possible to achievecompactness, configuration simplification and the like for the maintransmission apparatus 32 through a reduction in the number of parts.

Also, in this main transmission apparatus 32, among the four speedchange gear sets 56 to 59, the second speed change gear 56B of thetwo-speed gear set 57 also serves as the first deceleration gear 65A ofthe high-speed deceleration gear set 65 out of the two deceleration gearsets 64, 65. Accordingly, it is possible to achieve further compactness,configuration simplification and the like for the main transmissionapparatus 32 through a reduction in the number of parts.

As shown in FIG. 8, in the main transmission apparatus 32, the threetransmission shafts 51 to 53 that are arranged parallel with each otherare arranged so as to substantially form an isosceles triangle havingthe second transmission shaft 52 (intermediate shaft) as the uppervertex, in a view in the front-rear direction of the vehicle body.

Accordingly, in the main transmission apparatus 32, the firsttransmission shaft 51 and the third transmission shaft 53, which areheavier due to the four speed change multi-disc clutches 60 to 63 andthe two deceleration multi-disc clutches 66, 67 being arrangedcoaxially, are arranged side-by-side in the right-left direction in thelower portion of the main transmission apparatus 32. Also, the secondtransmission shaft 52, which is lighter due to the speed changemulti-disc clutches 60 to 63 and the deceleration multi-disc clutches66, 67 not being arranged coaxially, is arranged at a position that isbetween the first transmission shaft 51 and the third transmission shaft53 and is higher the first transmission shaft 51 and the thirdtransmission shaft 53.

In other words, the main transmission apparatus 32 can be arranged inthe interior space of the second case 22 with a low center of gravityand improved balance in the right-left direction. As a result, it ispossible to improve the stability of the tractor that is equipped withthe transmission 3 that includes this main transmission apparatus 32.

As shown in FIG. 8, in the main transmission apparatus 32, among thethree transmission shafts 51 to 53 that are arranged parallel with eachother, in the case of the second transmission shaft 52 (intermediateshaft) in which the speed change multi-disc clutches 60 to 63 and thedeceleration multi-disc clutches 66, 67 are not arranged coaxially, thesecond transmission shaft 52 is inserted in an upper space 90 out of apair of upper and lower virtual spaces 90, 91 in the approximatetriangular shape formed by the speed change multi-disc clutches 60 to 63and the deceleration multi-disc clutches 66, 67.

Specifically, in a front view of the vehicle body, in the case offorming a pair of triangular virtual spaces that each has one side thatis a virtual line interconnecting the axis of the first transmissionshaft 51 (speed change shaft) and the axis of the third transmissionshaft 53 (deceleration shaft) and are above and below that virtual line(these triangles have a larger height than the aforementioned isoscelestriangle, and being equilateral triangles for example), the secondtransmission shaft 52 (intermediate shaft) is located inside the one(here, the upper) virtual space 90. This is referred to as being“inserted” in this specification. Note that in the followingdescription, the virtual spaces 90, 91 will be simply referred to as“spaces 90, 91”.

Accordingly, it is possible to shorten the up-down length of the maintransmission apparatus 32, and it is possible to shorten the up-downlength of the transmission 3 that includes this main transmissionapparatus 32. As a result, it is possible to lower the height positionof the driver portion 2 arranged above the transmission 3, and it ispossible to lower the vehicle height of the tractor.

Also, as previously described, the second transmission shaft 52 is acylinder shaft that is relatively rotatably fitted around the upstreamrelay shaft 42 of the work transmission system 20, and therefore theupstream relay shaft 42 is also inserted into the upper space 90 formedbetween the speed change multi-disc clutches 60 to 63 and thedeceleration multi-disc clutches 66, 67. Accordingly, it is possible toarrange the upstream relay shaft 42 in the interior space of the secondcase 22 without retaining an arrangement space that is solely for thepassage of the upstream relay shaft 42.

As shown in FIG. 8, among the three transmission shafts 51 to 53, thefirst transmission shaft 51 and the third transmission shaft 53 arearranged separately in the right-left direction such that the axesthereof are in a substantially right/left symmetrical positionalrelationship with respect to a line that connects the axis of the secondtransmission shaft 52 and the axis of at least one of the front wheeltransmission shaft 80 and the first output shaft 16.

Arrangement of Multi-Disc Clutches

As shown in FIG. 8, in the drive switching unit 37, the constant speedtransmission multi-disc clutch 84, and the acceleration transmissionmulti-disc clutch 86 are arranged below the main transmission apparatus32 in a state where the upper portion sides thereof are inserted intothe lower space 91 formed between the speed change multi-disc clutches60 to 63 and the deceleration multi-disc clutches 66, 67.

Accordingly, it is possible to shorten the up-down length of the secondcase 22 having the interior space in which the main transmissionapparatus 32 and the drive switching unit 37 are arranged, and it ispossible to shorten the up-down length of the transmission 3 thatincludes these parts. As a result, it is possible to lower the heightposition of the driver portion 2 arranged above the transmission case14, and it is possible to lower the vehicle height of the tractor.

Also, the constant speed transmission multi-disc clutch 84 and thedeceleration transmission multi-disc clutch 86 are arranged below themain transmission apparatus 32, thus making it possible to achieve alower center of gravity for the transmission 3 that includes the maintransmission apparatus 32 and the drive switching unit 37, in comparisonwith the case where the multi-disc clutch 84 and 86 are arranged abovethe main transmission apparatus 32. As a result, it is possible toimprove the stability of the tractor that includes this transmission 3.

Detailed Configuration of Multi-Disc Clutches

As shown in FIGS. 2 to 5 and 8, among the previously-described fivetransmission switching apparatuses (31, 32, 44, 81, 82), theforward/rearward switchover apparatus 31, the main transmissionapparatus 32, the first drive switching apparatus 81 and the seconddrive switching apparatus 82, which are included in the travelingtransmission system 19, are arranged in the interior space of the secondcase 22 as transmission switching apparatuses for traveling. On theother hand, the work motive power switching apparatus 44 included in thework transmission system 20 is arranged in the interior space of thefourth case 24 as a transmission switching apparatus for work.

In other words, in this transmission 3, the transmission switchingapparatuses for travel that have the multi-disc clutches 45, 46, 60 to63, 66, 67, 84 and 86 that are engaged and disengaged byelectro-hydraulic control (i.e., the forward/rearward switchoverapparatus 31, the main transmission apparatus 32, the first driveswitching apparatus 81 and the second drive switching apparatus 82) arearranged in a grouped manner in the interior space in the second case22, and therefore the hydraulic operation systems for these transmissionswitching apparatuses for travel (31, 32, 81, 82) can be easilyconfigured in a grouped state in the second case 22.

In the forward/rearward switchover apparatus 31, the main transmissionapparatus 32, the first drive switching apparatus 81 and the seconddrive switching apparatus 82, which are provided as transmissionswitching apparatuses for travel, the diameter-direction sizes(diameters) of the multi-disc clutches 45, 46, 60 to 63, 66, 67, 84 and86 provided in all of these apparatuses are set to the same size.

Accordingly, clutch plates (drive plates and driven plates) 92, pressureplates 93, pistons 94 and the like that are used in the multi-discclutches 45, 46, 60 to 63, 66, 67, 84 and 86 can be common parts thatare used in common in the multi-disc clutches 45, 46, 60 to 63, 66, 67,84 and 86 that all have the same diameter-direction size. As a result,it is possible to facilitate parts management, for example.

Also, when controlling the engagement and disengagement operations ofthe multi-disc clutches 45, 46, 60 to 63, 66, 67, 84 and 86 byelectro-hydraulic control, given that the pistons 94 and the like arecommon parts, by setting the same initial pressure for the multi-discclutches 45, 46, 60 to 63, 66, 67, 84 and 86, it is possible to set thesame clutch meet timing for the multi-disc clutches 45, 46, 60 to 63,66, 67, 84 and 86. As a result, it is easier to create various controlprograms that are necessary for appropriately controlling the engagementand disengagement operations of the multi-disc clutches 45, 46, 60 to63, 66, 67, 84 and 86 by electro-hydraulic control.

In the traveling transmission system 19, the deceleration multi-discclutch 66 on the low speed side provided in the second transmissionmechanism 55 of the main transmission apparatus 32 engages anddisengages high-torque motive power for travel that has been deceleratedby the deceleration gear set 64 on the low speed side in the maintransmission apparatus 32 and is to be branched into motive power forfront wheel driving and motive power for rear wheel driving, andtherefore the deceleration multi-disc clutch 66 has a stricter loadcondition than the other multi-disc clutches 45, 46, 60 to 63, 67, 84and 86 that are provided in the forward/rearward switchover apparatus31, the main transmission apparatus 32, the first drive switchingapparatus 81 and the second drive switching apparatus 82.

In the forward/rearward switchover apparatus 31, the main transmissionapparatus 32, the first drive switching apparatus 81 and the seconddrive switching apparatus 82, the diameter-direction sizes of themulti-disc clutches 45, 46, 60 to 63, 66, 67, 84 and 86 provided in allof these apparatuses are set to the same size, which is a size that isappropriate for the deceleration multi-disc clutch 66 on the low speedside that has the strictest load condition.

Accordingly, it is possible to reduce the number of clutch plates 92provided in the other multi-disc clutches 45, 46, 60 to 63, 67, 84 and86 that have more leeway in terms of the load condition than thedeceleration multi-disc clutch 66 on the low speed side does, and it ispossible to shorten the axial-direction (vehicle body front-reardirection) length of these other multi-disc clutches. Also, it ispossible to shorten the vehicle body front-rear direction lengths of theforward/rearward switchover apparatus 31, the main transmissionapparatus 32, the first drive switching apparatus 81 and the seconddrive switching apparatus 82 that include the multi-disc clutches 45,46, 60 to 63, 67, 84 and 86, for which the axial-direction length can beshortened, and it is possible to shorten the front-rear length of thetransmission 3 that includes these apparatuses. As a result, it ispossible to prevent an increase in the size of the tractor, whichincreases in overall length due to an increase in the front-rear lengthof the transmission 3.

Also, in the above configuration, the multi-disc clutches 45, 46, 60 to63, 66, 67, 84 and 86 have an increased diameter-direction size,therefore increasing the size of the pair of upper and lower spaces 90,91 having an approximately triangular shape formed between the speedchange multi-disc clutches 60 to 63 and the deceleration multi-discclutches 66, 67. Accordingly, the second transmission shaft 52 and theupstream relay shaft 42, which are to be inserted into the upper space90 as previously described, can be inserted more deeply into the upperspace 90. Also, in the case of the constant speed transmissionmulti-disc clutch 84 and the acceleration transmission multi-disc clutch86, which are to be inserted into the lower space 91 as previouslydescribed, the upper portion sides thereof can be inserted more deeplyinto the lower space 91.

As a result, it is possible to set the diameter-direction sizes of themulti-disc clutches 45, 46, 60 to 63, 66, 67, 84 and 86 to the samesize, which is the size appropriate for the deceleration multi-discclutch 66 on the low speed side that has the strictest load condition,while also suppressing the problem of an increase in the up-down lengthof the transmission 3 that includes these multi-disc clutches.

Incidentally, in the main transmission apparatus 32, the decelerationmulti-disc clutch 66 on the low speed side and the decelerationmulti-disc clutch 67 on the high speed side engage and disengagehigh-torque motive power for travel that has been decelerated by thelow-speed deceleration gear set 64 or the high-speed deceleration gearset 65, and therefore these deceleration multi-disc clutches 66, 67 havea stricter load condition than the speed change multi-disc clutches 60to 63 that engage and disengage motive power for travel that has notbeen decelerated and has a smaller torque. For this reason, if thediameter-direction sizes of the multi-disc clutches 60 to 63, 66, 67provided in the main transmission apparatus 32 are set to the same sizeas described above, the deceleration multi-disc clutches 66, 67 willhave a larger number of clutch plates 92 than the speed changemulti-disc clutches 60 to 63, and the axial-direction (vehicle bodyfront-rear direction) lengths thereof will increase.

In view of this, in the main transmission apparatus 32, the four speedchange multi-disc clutches 60 to 63 having a shorter axial-directionlength are arranged coaxially with the first transmission shaft 51 andadjacent in the front-rear direction. Also, the two decelerationmulti-disc clutches 66, 67 that have a longer axial-direction length arearranged coaxially with the third transmission shaft 53 and adjacent inthe front-rear direction.

Accordingly, the front-rear length of the main transmission apparatus 32can be set shorter than in the case where, for example, two of the fourspeed change multi-disc clutches 60 to 63 that have a shorteraxial-direction length are arranged coaxially with the firsttransmission shaft 51 and adjacent in the front-rear direction, and theremaining two are arranged adjacent in the front-rear direction andcoaxially with the third transmission shaft 53 and the two decelerationmulti-disc clutches 66, 67 that have a longer axial-direction length. Asa result, it is possible to shorten the front-rear length of thetransmission 3 that includes this main transmission apparatus 32, and itis possible to prevent an increase in the size of the tractor thatincludes this transmission 3, which tends to increase in overall length.

As shown in FIGS. 4 and 5, in the multi-disc clutches 45, 46, 60 to 63,66, 67, 84 and 86 that have an increased diameter as previouslydescribed, the piston 94 does not have an increased diameter overall,but rather is given a stepped shape in which only a pressing portion 94Afor pressing the clutch plate 92 has an increased diameter.

Accordingly it is possible to prevent a reduction in the response of thepiston 94 that occurs due to an increase in the volume of the piston 94in the case where the overall diameter of the piston 94 is increased. Itis also possible to prevent the centrifugal force that is generatedduring rotation of the piston 94 from increasing due to an increase inthe volume of the piston 94, thus making it possible to employ a weaker,smaller-diameter spring as a return spring 95 that requires spring forcefor overcoming this centrifugal force.

As shown in FIGS. 2 to 5, in the forward/rearward switchover apparatus31, the forward multi-disc clutch 45 and the rearward multi-disc clutch46 that are adjacent in the front-rear direction share a single clutchhousing 96. In the main transmission apparatus 32, among the four speedchange multi-disc clutches 60 to 63, the first-speed multi-disc clutch60 and the second-speed multi-disc clutch 61 that are adjacent in thefront-rear direction share a single clutch housing 97, and thethird-speed multi-disc clutch 62 and the fourth-speed multi-disc clutch63 share a single clutch housing 98. Also, the two decelerationmulti-disc clutches 66, 67 that are adjacent in the front-rear directionshare a single clutch housing 99.

Accordingly, the multi-disc clutches 45, 46, 60 to 63, 66, 67 that areadjacent in the front-rear direction share the clutch housings 97 to 99,thus making it possible to achieve compactness in the front-reardirection for the forward/rearward switchover apparatus 31 and the maintransmission apparatus 32, as well as improve the ease of assembly byreducing the number of parts, for example.

In the forward/rearward switchover apparatus 31, the main transmissionapparatus 32, the first drive switching apparatus 81 and the seconddrive switching apparatus 82, the clutch housings 96 to 99 and clutchhubs 100 to 103 have a length that allows for the addition of the clutchplates 92.

Accordingly, even in the case of, for example, another tractor that hasstricter load conditions due to including an engine 9 having a highhorsepower, the forward/rearward switchover apparatus 31, the maintransmission apparatus 32, the first drive switching apparatus 81 andthe second drive switching apparatus 82 included in the transmission 3can be easily adjusted to accommodate by the addition of the clutchplates 92, without inviting an increase in the size of the transmission3. In other words, this transmission 3 can be made highly versatile soas to also be employable in other tractors having variousspecifications.

Detailed Configuration of Drive Switching Unit

As shown in FIG. 2, in the first drive switching apparatus 81 of thedrive switching unit 37, a first deceleration gear 83A of thedeceleration gear set 83, the constant speed transmission multi-discclutch 84 and the like that are arranged coaxially with the front wheeltransmission shaft 80 are configured as a unit with the front wheeltransmission shaft 80. In the second drive switching apparatus 82, afirst acceleration gear 85A of the acceleration gear set 85, theacceleration transmission multi-disc clutch 86 and the like that arearranged coaxially with the front wheel transmission shaft 80 areconfigured as a unit.

In other words, in the drive switching unit 37, the first driveswitching apparatus 81 and the second drive switching apparatus 82 areseparately configured as units in a state of excluding a seconddeceleration gear 83B of the deceleration gear set 83 and a secondacceleration gear 85B of the acceleration gear set 85 that are arrangedcoaxially with the first output shaft 16.

Accordingly, in this drive switching unit 37, the acceleration gear set85 can be arranged between the first drive switching apparatus 81 andthe second drive switching apparatus 82, and the acceleration gear set85 does not need to be arranged rearward of the second drive switchingapparatus 82 as in the case where the first drive switching apparatus 81and the second drive switching apparatus 82 are configured as anintegrated unit.

As a result, it is possible to shorten the separation distance betweenthe acceleration gear set 85 and the deceleration gear set 83 that isarranged on the vehicle body front side of the first drive switchingapparatus 81, and it is possible to shorten the front-rear length of thefirst output shaft 16, which the second deceleration gear 83B of thedeceleration gear set 83 and the second acceleration gear 85B of theacceleration gear set 85 are arranged coaxially with, and shorten thefront-rear length of the fifth case 25 that supports the first outputshaft 16. Accordingly, it is possible to reduce the weight of thetransmission 3 that includes these members, for example.

As shown in FIG. 2, the drive switching unit 37 includes the seconddrive switching apparatus 82 that is configured as a unit as describedabove, and that is removably attached to the front wheel transmissionshaft 80.

Accordingly, by performing the simple operation of attaching/removingthe unit-configured second drive switching apparatus 82 to/from thefront wheel transmission shaft 80, it is possible to easily changespecifications between a standard specification in which by includingonly the first drive switching apparatus 81 it is possible to switch thedrive switching unit 37 between a two-wheel drive state and a four-wheeldrive state, and a front wheel acceleration specification in which byincluding the first drive switching apparatus 81 and the second driveswitching apparatus 82 it is possible to switch between a two-wheeldrive state, a four-wheel drive state, and a front wheel accelerationstate. As a result, it is possible to improve the versatility of thistransmission 3.

As shown in FIG. 2, the second deceleration gear 83B and the secondacceleration gear 85B are arranged in a state of integrally rotatingcoaxially with the first output shaft 16, and thus the first outputshaft 16 is configured to be capable of being used with both thestandard specification (not-attached specification) in which the seconddrive switching apparatus 82 is not attached, and the front wheelacceleration specification (attached specification) in which the seconddrive switching apparatus 82 is attached.

Accordingly, the first output shaft 16 does not need to be replaced whenchanging the specification of the drive switching unit 37 between thestandard specification and the front wheel acceleration specification.As a result, it is possible to easily change the specification of thedrive switching unit 37.

Although not shown, this tractor includes an electronic control unitthat outputs various types of control instructions such as aforward/rearward switching instruction, a speed change instruction, anda front wheel drive switching instruction based on operations performedon a forward/rearward switching lever, a main gearshift lever, a frontwheel drive selection switch, a diff-lock pedal and the like that areprovided in the driver portion 2.

Hydraulic Devices

As shown in FIGS. 2, 3 and 8, in this tractor, the forward/rearwardswitchover apparatus 31, the main transmission apparatus 32, the driveswitching unit 37, the rear wheel differential apparatus 38, the frontwheel differential apparatus (not shown), etc. are electro-hydrauliccontrolled hydraulic devices that operate under control of an electroniccontrol unit. Among these hydraulic devices, the forward/rearwardswitchover apparatus 31, the main transmission apparatus 32, the driveswitching unit 37, the rear wheel differential apparatus 38, etc. areprovided inside the transmission case 14.

As shown in FIGS. 2, 3 and 9, the transmission 3 includes: a pump unit104 that supplies pressurized oil stored inside the transmission case 14to the hydraulic devices such as the forward/rearward switchoverapparatus 31; and a valve unit 105 that controls the flow of oil to thehydraulic devices such as the forward/rearward switchover apparatus 31.

If the pump unit 104 and the valve unit 105 were arranged in the upperend portion of the transmission case 14, due to vibration duringtraveling, the pump unit 104 and the valve unit 105 could come intocontact with the cabin 11 that is supported on the transmission 3 in avibration-controlled manner. Therefore, the pump unit 104 and the valveunit 105 are arranged in the right side portion of the transmission case14 to avoid such contact. Also, since the right side portion of thetransmission case 14 is a lateral side portion that is open toward theoutside and thus not adjacent to the fuel tank 4 (remote from the fueltank 4), maintenance can be easily performed on the pump unit 104 andthe valve unit 105.

As shown in FIGS. 2, 3, 9 and 10, the transmission case 14 has a pumpunit attachment portion 106 for attachment of the pump unit 104 from theouter right side, and a valve unit attachment portion 107 for attachmentof the valve unit 105 from the outer right side of the transmission case14. The pump unit attachment portion 106 protrudes outward to the rightfrom the right side portion of the third case 23 in the transmissioncase 14. The valve unit attachment portion 107 is formed in the rightside portion of the second case 22 in the transmission case 14.

As shown in FIGS. 2 and 3, the pump unit 104 has a duplex firsthydraulic pump 104A that is attached to the front end of the pump unitattachment portion 106, and a second hydraulic pump 104B that isattached to the rear end of the pump unit attachment portion 106. Thefirst hydraulic pump 104A and the second hydraulic pump 104B are drivenby motive power transmitted from the work transmission system 20 via apump driving gear set 108. The pump driving gear set 108 includes: afirst gear 108A that also serves as a coupling for interlockinglyjoining the upstream relay shaft 42 and the downstream relay shaft 43 ofthe work transmission system 20; and a second gear 108B for relay; andfurther a third gear 108C for output.

Valve Unit

As shown in FIGS. 3, 9, 11 and 12, the valve unit 105 includes: a baseplate 110 to which the valve unit attachment portion 107 is attached;and a first valve block 111 and a second valve block 112 that havemultiple electromagnetic valves.

The first valve block 111 includes, each acting as one of a plurality ofelectromagnetic valves, a forward-travel electromagnetic on/off valve113 for switching the flow of oil with respect to the forward multi-discclutch 45; a rearward-travel electromagnetic on/off valve 114 forswitching the flow of oil with respect to the rearward multi-disc clutch46; a first-speed electromagnetic on/off valve 115 for switching theflow of oil with respect to the first-speed multi-disc clutch 60; asecond-speed electromagnetic on/off valve 116 for switching the flow ofoil with respect to the second-speed multi-disc clutch 61; a third-speedelectromagnetic on/off valve 117 for switching the flow of oil withrespect to the third-speed multi-disc clutch 62; a fourth-speedelectromagnetic on/off valve 118 for switching the flow of oil withrespect to the fourth-speed multi-disc clutch 63; a constant speedtransmission electromagnetic on/off valve 119 for switching the flow ofoil with respect to the constant speed transmission multi-disc clutch84; an acceleration transmission electromagnetic on/off valve 120 forswitching the flow oil with respect to the acceleration transmissionmulti-disc clutch 86; a rear wheel differential electromagnetic on/offvalve 121 for switching the flow of oil with respect to the differentialswitching mechanism 38B of the rear wheel differential apparatus 38; anda front wheel differential electromagnetic on/off valve 122 forswitching the flow of oil with respect to the differential switchingmechanism of the front wheel differential apparatus.

The second valve block 112 includes, each acting as one of a pluralityof electromagnetic valves, a forward/rearward electromagneticproportional valve 123 that performs continuous control of the flow ofoil with respect to the forward multi-disc clutch 45 and the rearwardmulti-disc clutch 46; a low-speed electromagnetic proportional valve 124that performs continuous control of the flow of oil with respect to thedeceleration multi-disc clutch 66 on the low speed side out of the twodeceleration multi-disc clutches 66, 67; and a high-speedelectromagnetic proportional valve 125 that performs continuous controlof the flow of oil with respect to the deceleration multi-disc clutch 67on the high-speed side out of the two deceleration multi-disc clutches66, 67.

Although not shown, internal oil passages related to electro-hydrauliccontrol of the forward/rearward switchover apparatus 31, the maintransmission apparatus 32, the drive switching unit 37, etc. are formedin the base plate 110, the first valve block 111 and the second valveblock 112.

Valve Unit Attachment Portion

As shown in FIGS. 9 to 11, the valve unit attachment portion 107 isprovided with a recessed portion 107A that defines and forms a storagecompartment 126 for the first valve block along with the base plate 110.The first valve block 111 is attached to a storage compartment formingsurface 110A that forms the storage compartment 126 between the baseplate 110 and the recessed portion 107A of the valve unit attachmentportion 107. The second valve block 112 is attached to an outer surface110B of the base plate 110 that that is on the side opposite to thestorage compartment forming surface 110A.

According to this configuration, the valve unit 105 is configured suchthat, when attached to the valve unit attachment portion 107 of thetransmission case 14, the first valve block 111, which has the ten (10)electromagnetic on/off valves 113 to 122, is stored inside the storagecompartment 126 that is formed separately from the interior space of thetransmission case 14 in the right side portion of the transmission case14. Also, the second valve block 112, which has the three (3)electromagnetic proportional valves 123 to 125, is arranged at aposition laterally outward of the storage compartment 126 in the rightside portion of the transmission case 14.

According to the above configuration, it is possible to prevent ironpowder or the like contained in the oil stored inside the transmissioncase 14 from being drawn toward the valve unit 105 by excitation of theelectromagnetic on/off valves 113 to 122 and the electromagneticproportional valves 123 to 125. As a result, it is possible to avoid therisk that, due to this drawing, the iron powder or the like contained inthe oil inside the transmission case 14 enters the valve unit 105 andbecomes lodged in any one of the electromagnetic on/off valves 113 to122 and the electromagnetic proportional valves 123 to 125.

Also, there is no need for an opening for allowing the first valve block111 to enter the interior space of the transmission case 14 to be formedin the valve unit attachment portion 107, unlike the case where thefirst valve block 111 is arranged in the interior space of thetransmission case 14, thus making it possible to prevent a reduction inthe strength of the transmission case 14 caused by the formation of suchan opening.

Also, the first valve block 111, which has the electromagnetic on/offvalves 113 to 122 that have a high risk of oil leakage, is stored in thestorage compartment 126, and the second valve block 112, which has theelectromagnetic proportional valves 123 to 125 that have a low risk ofoil leakage, are arranged outside of the transmission case 14, andtherefore it is possible to reduce the size of the recessed portion 107Aof the transmission case 14 for forming the storage compartment, andalso increase the size of the interior space of the transmission case14, while also preventing the leakage of oil to the outside. As aresult, it is easier to perform arrangement, assembly and the like ofthe traveling transmission system 19, the work transmission system 20and the like that are to be arranged in the interior space of thetransmission case 14.

When the valve unit 105 is attached to the valve unit attachment portion107 of the transmission case 14, the attachment height position thereofis set such that the upper end portion of at least the first valve block111 is located higher than the height position of the oil surface of theoil stored inside the transmission case 14.

Oil Return Passages of Valve Unit Attachment Portion

As shown in FIGS. 3 and 9 to 11, the valve unit attachment portion 107is provided with seven (7) oil return passages 107B for returning excessoil from the first valve block 111 to the inside of the transmissioncase 14, at positions higher, with respect to the vehicle body verticaldirection, than the first valve block 111 in the recessed portion 107A.

Accordingly, oil that has leaked from the electromagnetic on/off valves113 to 122 of the first valve block 111 can be stored, as lubricatingoil, up to a position in the storage compartment 126 higher, withrespect to the vehicle body vertical direction, than the first valveblock 111. After the oil surface of this lubricating oil reaches thelevel each of the oil return passages of the storage compartment 126,the lubricating oil coming to the oil return passages can be returned,as excess oil, to the inside of the transmission case 14 via the oilreturn passages 107B. It is also possible to make it unlikely for aproblem to occur in which oil stored inside the transmission case 14, aswell as iron powder or the like contained in such oil, flows from theoil return passages 107B into the storage compartment 126 due to largeinclination of the tractor or the like.

As shown in FIGS. 9 to 11, the seven oil return passages 107B are formedseparated into two sections vertically in the valve unit attachmentportion 107. Accordingly, compared to the case where all of the oilreturn passages 107B are formed at the same height position, it ispossible to make it unlikely for a problem to occur in which oil storedinside the transmission case 14, as well as iron powder or the likecontained in such oil, flows from the oil return passages 107B into thestorage compartment 126.

Among the oil return passages 107B that are formed in two sectionsvertically, three (3) oil return passages 107B are formed in the uppersection, and four (4) oil return passages 107B are formed in the lowersection, and therefore the total opening area of the oil return passages107B in the upper section is smaller than the total opening area of theoil return passages 107B in the lower section.

This configuration is employed in consideration of the fact that in thecase where the oil return passages 107B are formed in two sectionsvertically, a majority of the excess oil returns to the transmissioncase 14 via the oil return passages 107B in the lower section, and theoil return passages 107B in the upper section are used as auxiliarypassages for the case where a large amount of oil leaks from theelectromagnetic on/off valves 113 to 122 for example, and thus makes itpossible to prevent a reduction in the strength of the transmission case14 that occurs due to unnecessarily increasing the total opening area ofthe oil return passages 107B in the upper section that are used asauxiliary passages.

As shown in FIGS. 3, 9 and 11, an oil filter 127 is provided in each ofthe oil return passages 107B. Accordingly, even if oil stored inside thetransmission case 14 flows through the oil return passages 107B to thestorage compartment 126, it is possible to prevent iron powder or thelike contained in such oil from flowing into the storage compartment126. Also, because the seven (7) oil return passages 107B are formed intwo sections vertically as previously described, in the case where clogsform at the oil filters 127 provided in the oil return passages 107B inthe lower section, excess oil in the storage compartment 126 can bereturned to the inside of the transmission case 14 through the oilreturn passages 107B in the upper section.

Recessed Portion of Valve Unit Attachment Portion

As shown in FIGS. 9 to 11, in the valve unit attachment portion 107, therecessed portion 107A has a lower recession portion 107 a for storingthe first valve block 111, and an upper recession portion 107 b that isin communication with the inside of the transmission case 14 via the oilreturn passages 107B. The upper recession portion 107 b is formed so asto have a shallower recession depth than the lower recession portion 107a and have a smaller area than the lower recession portion 107 a.

Accordingly, the interior space of the transmission case 14 can belarger than in the case where, for example, the upper recession portion107 b not storing the first valve block 111 is formed so as to have thesame recession depth and area as the lower recession portion 107 a. As aresult, it is easier to perform arrangement, assembly and the like ofthe traveling transmission system 19, the work transmission system 20,etc. that are to be arranged in the interior space of the transmissioncase 14.

Although not shown, the input shaft 15 of the transmission 3 is providedwith a forward-travel oil passage that extends between the front portionof the input shaft 15 supported by the front cover 27 and the forwardmulti-disc clutch 45; a rearward-travel oil passage that extends betweenthe front portion of the input shaft 15 supported by the front cover 27and the rearward multi-disc clutch 46, etc. The front wheel transmissionshaft 80 of the drive switching unit 37 is provided with, aconstant-speed oil passage that extends between the rear end portion ofthe front wheel transmission shaft 80 supported by the first supportwall 28 and the constant speed transmission multi-disc clutch 84; and anacceleration oil passage that extends between the rear end portion ofthe front wheel transmission shaft 80 supported by the first supportwall 28 and the acceleration transmission multi-disc clutch 86, etc.

Oil Passages of Valve Unit Attachment Portion

As shown in FIGS. 4, 5 and 8 to 11, in the main transmission apparatus32, the three transmission shafts 51 to 53 are arranged such that thelower end of the second transmission shaft (intermediate shaft) 52 islocated higher, with respect to the vehicle body vertical direction,than the upper end of the first transmission shaft (speed change shaft)51 and the upper end of the third transmission shaft (decelerationshaft) 53, and such that the upper end of the first transmission shaft51 is located lower, with respect to the vehicle body verticaldirection, than the upper end of the third transmission shaft 53. Thefirst transmission shaft 51 is provided with: a first-speed oil passage51A that extends between the front end portion of the first transmissionshaft 51 supported by the partition wall 22B of the second case 22 andthe first-speed multi-disc clutch 60; a second-speed oil passage 51Bthat extends between the front end portion of the first transmissionshaft 51 supported by the partition wall 22B of the second case 22 andthe second-speed multi-disc clutch 61; a third-speed oil passage 51Cthat extends between the front end portion of the first transmissionshaft 51 supported by the partition wall 22B of the second case 22 andthe third-speed multi-disc clutch 62; a fourth-speed oil passage 51Dthat extends between the front end portion of the first transmissionshaft 51 supported by the partition wall 22B of the second case 22 andthe fourth-speed multi-disc clutch 63, etc. The third transmission shaft(deceleration shaft) 53 is provided with: a low-speed oil passage 53Athat extends between the front end portion of the third transmissionshaft 53 supported by the partition wall 22B of the second case 22 andthe deceleration multi-disc clutch 66 on the low speed side; ahigh-speed oil passage 53B that extends between the front end portion ofthe third transmission shaft 53 supported by the partition wall 22B ofthe second case 22 and the deceleration multi-disc clutch 67 on the highspeed side, etc.

The valve unit attachment portion 107 is formed at a predeterminedposition in the vehicle body front-rear direction at which the partitionwall 22B is formed in the second case 22 of the transmission case 14.The partition wall 22B is provided with: a first-speed inner oil passage22C that extends between a first-speed connection port 105A formed inthe valve unit 105 and the first-speed oil passage 51A formed in thefirst transmission shaft 51; a second-speed inner oil passage 22D thatextends between a second-speed connection port 105B formed in the valveunit 105 and the second-speed oil passage 51B formed in the firsttransmission shaft 51; a third-speed inner oil passage 22E that extendsbetween a third-speed connection port 105C formed in the valve unit 105and the third-speed oil passage 51C formed in the first transmissionshaft 51; a fourth-speed inner oil passage 22F that extends between afourth-speed connection port 105D formed in the valve unit 105 and thefourth-speed oil passage 51D formed in the first transmission shaft 51;a low-speed inner oil passage 22G that extends between a low-speedconnection port 105E formed in the valve unit 105 and the low-speed oilpassage 53A formed in the third transmission shaft 53; a high-speedinner oil passage 22H that extends between a high-speed connection port105F formed in the valve unit 105 and the high-speed oil passage 53Bformed in the third transmission shaft 53, etc.

Accordingly, in the formation of the six hydraulic passages for the maintransmission apparatus between the valve unit 105 and the multi-discclutches 60 to 63, 66, 67 of the main transmission apparatus 32, thereis no need to assemble hydraulic tubes inside the transmission case 14.Also, the inner oil passages 22C to 22H of the partition wall 22B thatextend between the valve unit 105 and the first transmission shaft 51 orthe third transmission shaft 53 can be formed with a simple straightshape and with a minimum length. As a result, it is possible to reducethe number of work steps required to form the hydraulic passages for themain transmission apparatus.

Also, due to forming the inner oil passages 22C to 22H of the partitionwall 22B with a simple straight shape and with a minimum length, the sixhydraulic passages for the main transmission apparatus between the valveunit 105 and the multi-disc clutches 60 to 63, 66, 67 of the maintransmission apparatus 32 can be formed with a simple shape and with aminimum length. As a result, this achieves an improvement in theresponse of the multi-disc clutches 60 to 63, 66, 67 in the maintransmission apparatus 32.

As shown in FIGS. 3 and 9, the valve unit attachment portion 107 isarranged nearer to the first transmission shaft 51 that supports thefour speed-change multi-disc clutches 60 to 63 than to the thirdtransmission shaft 53 that supports the two deceleration multi-discclutches 66, 67.

Accordingly, the number of long inner oil passages 22G and 22H formed inthe partition wall 22B can be set smaller than in the case where thevalve unit attachment portion 107 is arranged nearer to the thirdtransmission shaft 53 than to the first transmission shaft 51. As aresult, it is possible to prevent a reduction in the strength of thepartition wall 22B caused by an increase in the number of long inner oilpassages 22G and 22H that are formed in the partition wall 22B.

Detailed Configuration of Creep Transmission Apparatus

As shown in FIGS. 2, 3, 5 and 13, in the creep transmission apparatus33, the deceleration mechanism 69 includes: a deceleration shaft 130that is arranged parallel with the third transmission shaft 53 of themain transmission apparatus 32 and the first speed change shaft 68 ofthe auxiliary transmission apparatus 34; a first deceleration gear 71Athat is arranged coaxially with the third transmission shaft 53 in astate of rotating integrally with the third transmission shaft 53; asecond deceleration gear 71B and a third deceleration gear 72A that arearranged coaxially with the deceleration shaft 130 in a state ofrotating integrally with the deceleration shaft 130; and a fourthdeceleration gear 72B that is arranged coaxially with the first speedchange shaft 68 in a state of rotating relatively to the first speedchange shaft 68. Also, out of the two previously described decelerationgear sets 71, 72, the first deceleration gear 71A and the seconddeceleration gear 71B configure the deceleration gear set 71 that is onthe upstream side in the transmission direction and decelerates motivepower from the third transmission shaft 53 with a large transmissionratio and transmits it to the deceleration shaft 130. Also, out of thetwo previously described deceleration gear sets 71, 72, the thirddeceleration gear 72A and the fourth deceleration gear 72B configure thedeceleration gear set 72 that is on the downstream side in thetransmission direction and decelerates motive power from thedeceleration shaft 130 with a large transmission ratio and transmits itto the first speed change shaft 68.

In the deceleration mechanism 69, the first deceleration gear 71A iscoupled to the third transmission shaft 53, and the fourth decelerationgear 72B is coupled to the first speed change shaft 68.

The switching mechanism 70 includes: a first mesh-receiving rotatingbody 131 that is arranged coaxially with the third transmission shaft 53so as to rotate integrally with the third transmission shaft 53 in astate where movement in the axial direction relative to the thirdtransmission shaft 53 is allowed; a second mesh-receiving rotating body132 that is arranged coaxially with the first speed change shaft 68 soas to rotate relatively to the first speed change shaft 68 in a state ofrotating integrally with the fourth deceleration gear 72B; and a meshingrotating body 133 that is arranged coaxially with the first speed changeshaft 68 so as to rotate integrally with the first speed change shaft 68in a state where movement in the axial direction is allowed between aconstant speed position of meshing with the first mesh-receivingrotating body 131 and a deceleration position of meshing with the secondmesh-receiving rotating body 132. The switching mechanism 70 is coupledto the first speed change shaft 68 (see FIG. 13).

Accordingly, by coupling the switching mechanism 70 to the first speedchange shaft 68, it is possible to perform an operation check regardingwhether or not the meshing rotating body 133 is correctly moving withouta problem between the constant speed position of meshing with the firstmesh-receiving rotating body 131 and the deceleration position ofmeshing with the second mesh-receiving rotating body 132. Also, if aproblem occurs in this operation check, it is possible to resolve theproblem by, for example, finely adjusting the rotating bodies 131 to 133that are coupled to the first speed change shaft 68. As a result, it ispossible to facilitate the assembly operation, including the operationcheck of the switching mechanism 70.

Also, in this creep transmission apparatus 33, the first decelerationgear 71A of the deceleration mechanism 69 and the first mesh-receivingrotating body 131 of the switching mechanism 70 are formed independentlyof each other, and therefore the load acting on the first decelerationgear 71A does not have an influence on the first mesh-receiving rotatingbody 131. Accordingly, it is possible to avoid the risk of a decrease indurability of the first mesh-receiving rotating body 131 caused by theload acting on the first deceleration gear 71A having an influence onthe first mesh-receiving rotating body 131.

As shown in FIG. 13, the switching mechanism 70 is configured as a unitwith the fourth deceleration gear 72B. Accordingly, it is possible tofacilitate the attachment of the fourth deceleration gear 72B and theswitching mechanism 70 to the first speed change shaft 68 and theremoval therefrom.

As shown in FIGS. 2, 3, 5 and 13, the division position of the secondcase 22 and the third case 23 is set such that, at the arrangementlocation of the creep transmission apparatus 33, the transmission case14 is divided into the second case 22 on the upstream side in thetransmission direction that includes the third transmission shaft 53;and the third case 23 on the downstream side in the transmissiondirection that includes the first speed change shaft 68. In thedeceleration mechanism 69, only the first deceleration gear 71A iscoupled to the second case 22 along with the third transmission shaft53, and substantially the entirety of the deceleration mechanism 69,excluding the first deceleration gear 71A, is coupled to the third case23 along with the first speed change shaft 68 and the switchingmechanism 70.

Accordingly, in the case of attaching the creep transmission apparatus33 to the transmission case 14, the first deceleration gear 71A of thedeceleration mechanism 69 can be coupled to the second case 22 alongwith the third transmission shaft 53 and the like from the divided endside of the second case 22 on the third case 23 side. Also, theswitching mechanism 70 and substantially the entirety of thedeceleration mechanism 69, excluding the first deceleration gear 71A,can be coupled to the third case 23 along with the first speed changeshaft 68 and the like from the divided end side of the third case 23 onthe second case 22 side. Also, the second case 22 and the third case 23are coupled to each other such that the first mesh-receiving rotatingbody 131 coupled to the third case 23 is arranged coaxially with thethird transmission shaft 53 coupled to the second case 22, and such thatthe second deceleration gear 71B coupled to the third case 23 mesheswith the first deceleration gear 71A coupled to the second case 22,whereby the creep transmission apparatus 33 can be coupled to thetransmission case 14 in a state of extending between the thirdtransmission shaft 53 and the first speed change shaft 68. In otherwords, it is possible to facilitate the coupling of the creeptransmission apparatus 33 to the transmission case 14.

Also, in the case of removing the creep transmission apparatus 33 fromthe transmission case 14, by uncoupling the second case 22 and the thirdcase 23, and then separating the second case 22 and the third case 23,it is possible to divide the creep transmission apparatus 33 into thefirst deceleration gear 71A coupled to the second case 22 and theswitching mechanism 70 and substantially the entirety of thedeceleration mechanism 69 coupled to the third case 23, excluding thefirst deceleration gear 71A. Due to performing this division, the firstdeceleration gear 71A can be removed from the second case 22 along withthe third transmission shaft 53 and the like from the divided end sideof the second case 22 on the third case 23 side. Also, the switchingmechanism 70 and substantially the entirety of the decelerationmechanism 69, excluding the first deceleration gear 71A, can be removedfrom the third case 23 along with the first speed change shaft 68 andthe like from the divided end side of the third case 23 on the secondcase 22 side. In other words, it is possible to facilitate the removalof the creep transmission apparatus 33 from the transmission case 14,and thus facilitate maintenance of the creep transmission apparatus 33and the like.

As shown in FIGS. 2, 5 and 13, in the creep transmission apparatus 33,the front end portion of the deceleration shaft 130 is supported by thefirst support wall 28, and the rear end portion is supported by thefront end portion of the distributor shaft 35. The first decelerationgear 71A is splined to the rear portion of the third transmission shaft53, and is retained by a retainer ring 134. The second deceleration gear71B is splined to the front end side of the deceleration shaft 130. Thethird deceleration gear 72A is formed as a single piece with the rearend portion of the deceleration shaft 130. The first mesh-receivingrotating body 131 is spline-fitted to the rear end portion of the thirdtransmission shaft 53 in a state of being relatively rotatably supportedto a rotating body 135 that is spline-fitted to the front end portion ofthe first speed change shaft 68. The second mesh-receiving rotating body132 is engaged and coupled to the fourth deceleration gear 72B so as torotate integrally with the fourth deceleration gear 72B. The meshingrotating body 133 is spline-fitted to the outer circumferential portionof the rotating body 135. In other words, in the creep transmissionapparatus 33, the deceleration shaft 130, the second deceleration gear71B, and the third deceleration gear 72A are removably attached in thethird case 23 in a state of being configured as a unit, that is to say afirst unit 33A. Also, the fourth deceleration gear 72B, the firstmesh-receiving rotating body 131, the second mesh-receiving rotatingbody 132, the meshing rotating body 133, the rotating body 135 and thelike are removably attached in the third case 23 in a state of beingconfigured as a unit, that is to say a second unit 33B.

Another Embodiment of Creep Transmission Apparatus

FIGS. 14 and 15 show another embodiment of the creep transmissionapparatus 33 having a configuration that is different from that of thepreviously described creep transmission apparatus 33 in terms of thefirst deceleration gear 71A of the deceleration mechanism 69 and thefirst mesh-receiving rotating body 131 of the switching mechanism 70.

In the creep transmission apparatus 33 shown in FIG. 15, the firstdeceleration gear 71A of the deceleration mechanism 69 is arrangedcoaxially with the third transmission shaft 53 so as to rotateintegrally with the third transmission shaft 53 in a state wheremovement in the axial direction relative to the third transmission shaft53 is allowed. Also, the first deceleration gear 71A of the decelerationmechanism 69 and the first mesh-receiving rotating body 131 of theswitching mechanism 70 are formed as a single piece.

Accordingly, compared with the case where the first deceleration gear71A and the first mesh-receiving rotating body 131 are formedindependently from each other, it is possible to achieve configurationsimplification and the like through a reduction in the number of parts.

In the deceleration mechanism 69 and the switching mechanism 70 of thecreep transmission apparatus 33 shown in FIG. 15, the entirety of thedeceleration mechanism 69 and the entirety of the switching mechanism 70are coupled to the third case 23 along with the first speed change shaft68 such that the first deceleration gear 71A and the firstmesh-receiving rotating body 131 are arranged coaxially with the thirdtransmission shaft 53 in accordance with the coupling of the second case22 and the third case 23, and such that the first deceleration gear 71Aand the first mesh-receiving rotating body 131 are removed from thethird transmission shaft 53 in accordance with uncoupling of the secondcase 22 and the third case 23.

More specifically, as shown in FIGS. 2, 3, 14 and 15, in the creeptransmission apparatus 33, the deceleration mechanism 69 includes: thedeceleration shaft 130 that is arranged parallel with the thirdtransmission shaft 53 of the main transmission apparatus 32 and thefirst speed change shaft 68 of the auxiliary transmission apparatus 34;the first deceleration gear 71A that is arranged coaxially with thethird transmission shaft 53 so as to rotate integrally with the thirdtransmission shaft 53 in a state where movement in the axial directionrelative to the third transmission shaft 53 is allowed; the seconddeceleration gear 71B and the third deceleration gear 72A that arearranged coaxially with the deceleration shaft 130 in a state ofrotating integrally with the deceleration shaft 130; and the fourthdeceleration gear 72B that is arranged coaxially with the first speedchange shaft 68 in a state of relatively rotating with the first speedchange shaft 68. Also, out of the two previously described decelerationgear sets 71, 72, the first deceleration gear 71A and the seconddeceleration gear 71B configure the deceleration gear set 71 that is onthe upstream side in the transmission direction and decelerates motivepower from the third transmission shaft 53 with a larger transmissionratio and transmits it to the deceleration shaft 130. Moreover, out ofthe two previously described deceleration gear sets 71, 72, the thirddeceleration gear 72A and the fourth deceleration gear 72B configure thedeceleration gear set 72 that is on the downstream side in thetransmission direction and decelerates motive power from thedeceleration shaft 130 with a larger transmission ratio and transmits itto the first speed change shaft 68.

The switching mechanism 70 includes: the first mesh-receiving rotatingbody 131 that is arranged coaxially with the third transmission shaft 53so as to rotate integrally with the third transmission shaft 53 in astate where movement in the axial direction relative to the thirdtransmission shaft 53 is allowed; the second mesh-receiving rotatingbody 132 that is arranged coaxially with the first speed change shaft 68so as to rotate relatively to the first speed change shaft 68 in a stateof rotating integrally with the fourth deceleration gear 72B; and themeshing rotating body 133 that is arranged coaxially with the firstspeed change shaft 68 so as to rotate integrally with the first speedchange shaft 68 in a state where movement in the axial direction isallowed between the constant speed position of meshing with the firstmesh-receiving rotating body 131 and the deceleration position ofmeshing with the second mesh-receiving rotating body 132. The switchingmechanism 70 is coupled to the first speed change shaft 68 along withthe first deceleration gear 71A and the fourth deceleration gear 72B(see FIG. 15).

By coupling the switching mechanism 70 to the first speed change shaft68 in this way along with the first deceleration gear and the fourthdeceleration gear, it is possible to perform an operation checkregarding whether or not the meshing rotating body 133 is correctlymoving without a problem between the constant speed position of meshingwith the first mesh-receiving rotating body 131 and the decelerationposition of meshing with the second mesh-receiving rotating body 132.Also, if a problem occurs in this operation check, it is possible toresolve the problem by, for example, finely adjusting the rotatingbodies 131 to 133 that are coupled to the first speed change shaft 68.As a result, it is possible to facilitate the assembly operation,including the operation check of the switching mechanism 70.

As shown in FIGS. 2, 3, 14 and 15, the division position of the secondcase 22 and the third case 23 is set such that, at the arrangementlocation of the creep transmission apparatus 33, the transmission case14 is divided into the second case 22 on the upstream side in thetransmission direction that includes the third transmission shaft 53,and the third case 23 on the downstream side in the transmissiondirection that includes the first speed change shaft 68. In thedeceleration mechanism 69 and the switching mechanism 70, the entiretyof the deceleration mechanism 69 and the entirety of the switchingmechanism 70 are coupled to the third case 23 along with the first speedchange shaft 68 such that the first deceleration gear 71A and the firstmesh-receiving rotating body 131 are arranged coaxially with the thirdtransmission shaft 53 in accordance with the coupling of the second case22 and the third case 23, and such that the first deceleration gear 71Aand the first mesh-receiving rotating body 131 are removed from thethird transmission shaft 53 in accordance with uncoupling of the secondcase 22 and the third case 23.

Accordingly, in the case of attaching the creep transmission apparatus33 to the transmission case 14, the deceleration mechanism 69 and theswitching mechanism 70 can be coupled to the third case 23 along withthe first speed change shaft 68 and the like from the divided end sideof the third case 23 on the second case 22 side. Also, after thisattachment, the second case 22 and the third case 23 are coupled suchthat the first deceleration gear 71A and the first mesh-receivingrotating body 131 are arranged coaxially with the third transmissionshaft 53, and therefore the deceleration mechanism 69 and the switchingmechanism 70 can be coupled to the transmission case 14 in a state ofextending between the third transmission shaft 53 and the first speedchange shaft 68. In other words, the creep transmission apparatus 33 canbe easily attached in a state of extending between the thirdtransmission shaft 53 and the first speed change shaft 68 inside thetransmission case 14.

Also, in the case of removing the creep transmission apparatus 33 fromthe transmission case 14, by uncoupling the second case 22 and the thirdcase 23, and then separating the second case 22 and the third case 23,it is possible to remove the first deceleration gear 71A and the firstmesh-receiving rotating body 131 from the third transmission shaft 53,and it is possible to leave the entirety of the deceleration mechanism69 and the entirety of the switching mechanism 70 in the third case 23along with the first speed change shaft 68 and the like. Also, thedeceleration mechanism 69 and the switching mechanism 70 remaining inthe third case 23 can be removed from the third case 23 along with thefirst speed change shaft 68 and the like from the divided end side ofthe third case 23 on the second case 22 side. In other words, it ispossible to facilitate the removal of the creep transmission apparatus33 from the transmission case 14, and thus facilitate maintenance of thecreep transmission apparatus 33 and the like.

As shown in FIG. 15, in the creep transmission apparatus 33, the firstdeceleration gear 71A of the deceleration mechanism 69 and the firstmesh-receiving rotating body 131 of the switching mechanism 70 areformed as a single piece. Accordingly, compared with the case where thefirst deceleration gear 71A and the first mesh-receiving rotating body131 are formed independently from each other, it is possible to achieveconfiguration simplification and the like through a reduction in thenumber of parts.

As shown in FIGS. 2, 14 and 15, in the creep transmission apparatus 33,the front end portion of the deceleration shaft 130 is supported to thefirst support wall 28, and the rear end portion is supported to thefront end portion of the distributor shaft 35. The first decelerationgear 71A is spline-fitted to the rear portion of the third transmissionshaft 53 in a state of being formed as a single piece with the firstmesh-receiving rotating body 131. The second deceleration gear 71B isspline-fitted to the front end side of the deceleration shaft 130. Thethird deceleration gear 72A is formed as a single piece with the rearend portion of the deceleration shaft 130. The first mesh-receivingrotating body 131 is spline-fitted to the rear end portion of the thirdtransmission shaft 53 in a state of being relatively rotatably supportedto a rotating body 135 that is spline-fitted to the front end portion ofthe first speed change shaft 68. The second mesh-receiving rotating body132 is engaged and coupled to the fourth deceleration gear 72B so as torotate integrally with the fourth deceleration gear 72B. The meshingrotating body 133 is spline-fitted to the outer circumferential portionof the rotating body 135. In other words, in the creep transmissionapparatus 33, similarly to the previously described creep transmissionapparatus 33, the deceleration shaft 130, the second deceleration gear71B, and the third deceleration gear 72A are removably attached in thethird case 23 in a state of being configured as a unit, that is to saythe first unit 33A (see FIGS. 2 and 7). On the other hand, in this creeptransmission apparatus 33, unlike the previously described creeptransmission apparatus 33, the first deceleration gear 71A, the fourthdeceleration gear 72B, the first mesh-receiving rotating body 131, thesecond mesh-receiving rotating body 132, the meshing rotating body 133,the rotating body 135 and the like are removably attached in the thirdcase 23 in a state of being configured as a unit, that is to say thesecond unit 33B.

Arrangement of Main Transmission Apparatus and Auxiliary TransmissionApparatus in Divided Transmission Case

As shown in FIGS. 2, 3, 6, and 7, inside the transmission case 14, themain transmission apparatus 32 is arranged on the upstream side in thetransmission direction, and the auxiliary transmission apparatus 34 isarranged on the downstream side in the transmission direction. In thecase where the transmission case 14 is divided into the transmissionupstream side second case 22 with the main transmission apparatus 32 andthe transmission downstream side third case 23 with the auxiliarytransmission apparatus 34, an opening 136 is formed in the front end ofthe third case 23, which is the divided end of the third case 23 on thesecond case 22 side. Also, in the auxiliary transmission apparatus 34,the previously described output gear set 79 is exchangeably arranged ata position at the foremost end of the auxiliary transmission apparatus34 near the opening 136 of the third case 23.

Accordingly, in this tractor, by exchanging the output gear set 79 withanother output gear set 79 that has a different transmission ratio, itis possible to easily change and set the maximum speed of the tractor toa speed that is suited to, for example, the type of work to be performedby the user. Also, the output gear set 79 can be easily exchangedthrough the opening 136 of the third case 23, which is exposed when thetransmission case 14 is divided into the second case 22 and the thirdcase 23 for exchanging. In other words, by performing the simpleoperation of exchanging the output gear set 79 through the opening 136of the third case 23, it is possible to easily change and set themaximum speed of the tractor to a speed that is suited to, for example,the type of work to be performed by the user.

As previously described, the transmission case 14 is configured to bedivided into the second case 22 on the upstream side in the transmissiondirection and the third case 23 on the downstream side in thetransmission direction, at the arrangement location of the creeptransmission apparatus 33. The creep transmission apparatus 33 isattached at a position on the opening side inside the third case 23,which is a location that is adjacent to the output gear set 79 acrossthe second support wall 29. Also, the creep transmission apparatus 33 isremovably attached in the third case 23 in a state of being entirely orsubstantially entirely configured as units, namely the first unit 33Aand the second unit 33B.

Accordingly, in the case of exchanging the output gear set 79, first,the second case 22 and the third case 23 of the transmission case 14 areuncoupled, and then the second case 22 and the third case 23 areseparated. Next, the first unit 33A and the second unit 33B of the creeptransmission apparatus 33 arranged on the opening side of the third case23 are removed through the opening 136 of the third case 23 that isexposed due to the above separation, and thereafter the second supportwall 29 is removed to enable exchanging the output gear set 79 throughthe opening 136 of the third case 23. By exchanging the output gear set79 through the opening 136 of the third case 23, it is possible toeasily change and set the maximum speed of the tractor to a speed thatis suited to, for example, the type of work to be performed by the user.

In other words, with a configuration in which the creep transmissionapparatus 33 is arranged at the division location of the second case 22and the third case 23 in the transmission case 14, it is possible toeasily exchange the output gear set 79 through the opening 136 of thethird case 23, and it is possible to easily change and set the maximumspeed of the tractor to a speed that is suited to, for example, the typeof work to be performed by the user.

Other Embodiments

The present invention is not limited to the configurations described inthe above embodiment, and the following illustrates other representativeembodiments of the present invention. Note that the configurationsillustrated in the above embodiment can be combined with any one of theconfigurations of the following other embodiments as long as nocontradiction arises.

(1) The work vehicle transmission may have a configuration in which,including the work multi-disc clutch (PTO clutch) 87 provided in thework motive power switching apparatus 44 (one example of a transmissionswitching apparatus), the diameter-direction sizes of all of themulti-disc clutches 45, 46, 60 to 63, 66, 67, 84, 86 and 87 provided inthe transmission switching apparatuses (the forward/rearward switchoverapparatus 31, the main transmission apparatus 32, the work motive powerswitching apparatus 44, the first drive switching apparatus 81 and thesecond drive switching apparatus 82) are set to the same size.

(2) A configuration is possible in which the diameter-direction sizes ofthe multi-disc clutches 45, 46, 60 to 63, 66, 67, 84, 86 and 87 in thetransmission switching apparatuses (the forward/rearward switchoverapparatus 31, the main transmission apparatus 32, the work motive powerswitching apparatus 44, the first drive switching apparatus 81 and thesecond drive switching apparatus 82) are set to the same size, which issmaller than the size suited to the multi-disc clutch 66 that has thestrictest load condition.

(3) The configuration of the main transmission apparatus 32 can bemodified in various ways. For example, the main transmission apparatus32 may have a 12-speed configuration provided with six multi-discclutches for six speed changes and the two multi-disc clutches 66, 67for two speed changes, or an 18-speed configuration provided with sixmulti-disc clutches for six speed changes and three multi-disc clutchesfor three speed changes.

In other words, the number of speeds of the main transmission apparatus32 can be modified in various ways. For example, the main transmissionapparatus 32 may have a 12-speed configuration provided with the firsttransmission mechanism 54 that changes input motive power between sixspeeds, and the second transmission mechanism 55 that changes the motivepower changed by the first transmission mechanism 54 between two speeds,or an 18-speed configuration provided with the first transmissionmechanism 54 that changes input motive power between six speeds, and thesecond transmission mechanism 55 that changes the motive power changedby the first transmission mechanism 54 between three speeds.

(4) The work motive power switching apparatus 44 (one example of atransmission switching apparatus) may be configured to include amulti-disc clutch for work motive power speed change.

(5) The first drive switching apparatus 81 for front wheel driving andthe second drive switching apparatus 82 for front wheel acceleration maybe configured as an integrated unit.

(6) In the main transmission apparatus 32, the speed change multi-discclutches 60 to 63 may be arranged parallel with the decelerationmulti-disc clutches 66, 67 so as to be adjacent in the up-down(vertical) direction of the vehicle body (one example of the diameterdirection).

(7) In the main transmission apparatus 32, the three transmission shafts51 to 53 may be arranged so as to approximately form an isoscelestriangle having the intermediate shaft (the second transmission shaft52) as the lower vertex.

(8) In the main transmission apparatus 32, the diameter-direction sizesof the speed change multi-disc clutches 60 to 63 and the decelerationmulti-disc clutches 66, 67 may be set to different sizes.

(9) The main transmission apparatus 32 may be configured such that theintermediate shaft (the second transmission shaft 52) is inserted intothe lower space 91 out of the approximately triangular pair of upper andlower spaces 90, 91 formed between the speed change multi-disc clutches60 to 63 and the deceleration multi-disc clutches 66, 67.

(10) The main transmission apparatus 32 may be configured such that thelower portion side of the multi-disc clutches 84 and 86 in the driveswitching apparatus (first drive switching apparatus 81, second driveswitching apparatus 82) is inserted into the upper space 90 out of theapproximately triangular pair of upper and lower spaces 90, 91 formedbetween the speed change multi-disc clutches 60 to 63 and thedeceleration multi-disc clutches 66, 67.

(11) In the work vehicle transmission, the valve unit attachment portion107 may be formed in the left side portion of the transmission case 14,or the valve unit attachment portion 107 may be formed in each of theright and left side portions of the transmission case 14.

(12) The valve unit 105 may be configured such that the valve block 111having all of the electromagnetic valves (the electromagnetic on/offvalves 113 to 122, and the electromagnetic proportional valves 123 to125) included in the valve unit 105 is attached to the storagecompartment forming surface 110A of the base plate 110, and thus storedin the storage compartment 126.

(13) In the valve unit attachment portion 107, one oil return passage107B may be formed, or multiple oil return passages 107B may be formedin a series along the front-rear direction of the vehicle body.Alternatively, two oil return passages 107B having the same opening areamay be formed in two sections vertically.

(14) The auxiliary transmission apparatus 34 may be configured such thatthe output gear set 79 is located at the divided end of the downstreamcase (the third case 23) on the upstream case (the second case 22) side.

(15) Although the work vehicle is a tractor in the above embodiments,there is no limitation to this, and the work vehicle may be another workvehicle such as a mowing machine, a combine, a rice planter, or atransportation work vehicle.

What is claimed is:
 1. A work vehicle transmission comprising: aplurality of transmission shafts that extend parallel with each other ina front-rear direction of a vehicle body, the plurality of transmissionshafts including a speed change shaft and a deceleration shaft; and amulti-stage transmission apparatus including: a first transmissionmechanism configured to change input motive power to any one of aplurality of speeds, the first transmission mechanism having a pluralityof speed change gear sets, and a plurality of speed change multi-discclutches that are arranged adjacent in the front-rear direction on thespeed change shaft and engage and disengage power transmission to theplurality of speed change gear sets; and a second transmission mechanismconfigured to change motive power changed by the first transmissionmechanism to any one of a plurality of speeds, the number of speeds ofthe second transmission mechanism being smaller than the number ofspeeds of the first transmission mechanism, and the second transmissionmechanism having a plurality of deceleration gear sets, and a pluralityof deceleration multi-disc clutches that are arranged on thedeceleration shaft and engage and disengage power transmission to theplurality of deceleration gear sets, wherein the plurality of speedchange multi-disc clutches are arranged parallel with the plurality ofdeceleration multi-disc clutches so as to be adjacent in a diameterdirection thereof.
 2. The work vehicle transmission according to claim1, wherein the plurality of transmission shafts includes an intermediateshaft arranged between the speed change shaft and the decelerationshaft.
 3. The work vehicle transmission according to claim 2, whereinthe speed change shaft, the deceleration shaft and the intermediateshaft are arranged forming an isosceles triangle having the intermediateshaft as an upper vertex in a front view of the vehicle body.
 4. Thework vehicle transmission according to claim 1, whereindiameter-direction sizes of the plurality of speed change multi-discclutches and the plurality of deceleration multi-disc clutches are setto the same size.
 5. A work vehicle comprising the work vehicletransmission according to claim
 1. 6. A work vehicle transmissioncomprising: a plurality of transmission shafts that extend parallel witheach other in a front-rear direction of a vehicle body, the plurality oftransmission shafts including a speed change shaft and a decelerationshaft; and a multi-stage transmission apparatus including: a firsttransmission mechanism configured to change input motive power to anyone of a plurality of speeds, the first transmission mechanism having aplurality of speed change gear sets, and a plurality of speed changemulti-disc clutches that are arranged adjacent in the front-reardirection on the speed change shaft and engage and disengage powertransmission to the plurality of speed change gear sets; and a secondtransmission mechanism configured to change motive power changed by thefirst transmission mechanism to any one of a plurality of speeds, thenumber of speeds of the second transmission mechanism being smaller thanthe number of speeds of the first transmission mechanism, and the secondtransmission mechanism having a plurality of deceleration gear sets, anda plurality of deceleration multi-disc clutches that are arranged on thedeceleration shaft and engage and disengage power transmission to theplurality of deceleration gear sets, wherein the plurality oftransmission shafts further includes an intermediate shaft arrangedbetween the speed change shaft and deceleration shaft, the speed changemulti-disc clutches and the deceleration multi-disc clutches not beingarranged coaxially with the intermediate shaft, and in a front view ofthe vehicle body, assuming that there are formed a pair of triangularvirtual spaces that each has, as one side, a virtual lineinterconnecting an axis of the speed change shaft and an axis of thedeceleration shaft and that are above and below the virtual line, theintermediate shaft is inserted into one of the virtual spaces.
 7. Thework vehicle transmission according to claim 6, wherein the plurality ofspeed change multi-disc clutches and the plurality of decelerationmulti-disc clutches are arranged so as to be adjacent in a right-leftdirection of the vehicle body, and in a front view of the vehicle body,the pair of virtual spaces are respectively formed above and below aposition between the speed change multi-disc clutches and thedeceleration multi-disc clutches.
 8. The work vehicle transmissionaccording to claim 7, further comprising: a drive switching apparatusthat includes a multi-disc clutch and is configured to switch atransmission state with respect to right and left front wheels by anengaging/disengaging operation of the multi-disc clutch, wherein thedrive switching apparatus is arranged below the transmission apparatusin a state where an upper portion of the multi-disc clutch is insertedinto the virtual space on a lower side in the front view of the vehiclebody.
 9. The work vehicle transmission according to claim 6, whereindiameter-direction sizes of the plurality of speed change multi-discclutches and the plurality of deceleration multi-disc clutches are setto the same size.
 10. A work vehicle comprising the work vehicletransmission claim
 6. 11. A work vehicle transmission comprising: atransmission case that also serves as an oil tank; a plurality ofhydraulic devices arranged inside the transmission case; and a valveunit configured to control a flow of oil to the hydraulic devices,wherein the transmission case includes a valve unit attachment portionto which the valve unit is to be attached from outside the transmissioncase, the valve unit has a base plate to be attached to the valve unitattachment portion, and a valve block having a plurality ofelectromagnetic valves, and the valve unit attachment portion isprovided with a recessed portion that defines and forms a storagecompartment for the valve block along with the base plate.
 12. The workvehicle transmission according to claim 11, wherein the valve unitattachment portion includes an oil return passage configured to returnexcess oil from the valve block into the transmission case at a positionhigher, with respect to a vertical direction of the vehicle body, thanthe valve block in the recessed portion.
 13. The work vehicletransmission according to claim 12, wherein a plurality of the oilreturn passages are formed in two sections vertically in the valve unitattachment portion.
 14. The work vehicle transmission according to claim13, wherein the oil return passages are formed such that an opening areaof the oil return passage in an upper section is smaller than an openingarea of the oil return passage in a lower section.
 15. The work vehicletransmission according to claim 12, wherein the recessed portion has alower recession portion in which the valve block is stored, and an upperrecession portion that is in communication with an interior of thetransmission case via the oil return passage, and the upper recessionportion is formed with a shallower recession depth than the lowerrecession portion and a smaller area than the lower recession portion.16. The work vehicle transmission according to claim 12, wherein an oilfilter is provided in the oil return passage.
 17. The work vehicletransmission according to claim 11, wherein the plurality ofelectromagnetic valves includes a plurality of electromagnetic on/offvalves and a plurality of electromagnetic proportional valves, the valveblock includes a first valve block that has the plurality ofelectromagnetic on/off valves, and a second valve block that has theplurality of electromagnetic proportional valves, the first valve blockis attached to a storage compartment forming surface of the base platethat forms the storage compartment along with the recessed portion, andthe second valve block is attached to an outer surface of the base plateon a side opposite to the storage compartment forming surface.
 18. Thework vehicle transmission according to claim 11, wherein a partitionwall is formed as a single piece with the transmission case, thepartition wall supporting the plurality of transmission shafts providedin the transmission case, the plurality of hydraulic devices includes aplurality of transmission switching apparatuses arranged on theplurality of transmission shafts, the valve unit attachment portion isformed at a predetermined position in a front-rear direction of thevehicle body at which the partition wall is formed in the transmissioncase, and the partition wall is provided with a plurality of inner oilpassages that extend between a plurality of connection ports formed inthe valve unit and a plurality of oil passages formed in the pluralityof transmission shafts.
 19. A work vehicle comprising the work vehicletransmission according to claim 11.